new to C. need basic help

hey guys.
im new to programming and im having a bit of difficulty.


i am trying to store a value with the form fx.x. eg f1.2, f1.6 etc.
now the numbers 1.2, 1.6 need to be stored as floating point numbers,
but when print the value back out it has to be in the form f1.2, f1.6.
i also need to check for validity to make sure that the number entered is in the form fx

this is my code so far but at the moment i have no idea how to approach the next bit.
the value fx is the aperture.

Code:

---

#include <stdio.h>

int main(int argc, char ** argv)
{
  // Mainline Variable Declarations
  FILE * output = stdout;
  FILE * input = stdin;

  float  exposuretime;
  float aperture;


  fprintf(output,"please enter exposure time: ");
  fscanf(input,"%f",&exposuretime);

  fprintf(output,"please enter aperture value: ");


  fprintf(output,"the exposure time is: %f\n ",exposuretime);

}

---

You could just use the aperture value itself (e.g 1.4 or 5.6) without the f as input, and just output the value as f1.4

Alternatively, you will have to use a home-made parsing mechanism - the easiest version is something that reads a string, checks if the first letter is 'f' (or 'F'?), then passes the next element(s) of the string to sscanf() to extract your float number.

Of course, you'll still have to add the 'f' to the ouput.

--
Mats

Hmm, suspiciously similar to this thread ?

So basically you're trying to print out a float with a prefix? How about:

Code:

---


printf ("f%f\n", exposure);

---

and now apply similar logic to scanf...

QuantumPete

hmm. yeh

that would work.
i think i looked past that coz it seamed to simple lol.

umm. how would i check to see if its valid?

i would use an if statement.

but im not sure how to check it using that.

That depends on what you want to check for! Write out the constraints on paper first and the if statement will jump out at you ;-)

QuantumPete

Same answer as the other thread. Store them as strings. If you need to do math or something on the numbers, then convert them to floats/doubles... hint: strtod().

You don't need to store them as strings... scanf can extract the float part of the string during input and you simply re-add the 'f' for the output. That way, you don't need to parse or convert anything.

QuantumPete

One of the problems when attempting to validate data is to "know what's valid". The first step is to sort out comletely invalid values: f-stops can't be negative, and nore is zero a valid value. A sensible check would be 0.9 .. 40.0 as valid values, and anything else "invalid".

The next level of "more accurate checks" would be to validate that "this is a valid aperture value" - only certain values can be used as an aperture value. Since cameras use either half or 1/3 steps, not all values are actually "possible" apertures. Two full steps doubles the aperture number, e.g. 2.8 is two steps more open than 5.6. One step is 1.4 times the previous value (1.4 is from square-root of 2, which has to do with the fact that to get twice as much or half as much light through an area, you need to half the area, which as long as it's a square or circle, means multiplying/dividing each side by square-root of 2).

Half a step is approximately 1.2 (square root of 1.4), a third of a step is around 1.11 (cube root of 1.4).


--
Mats

ok.
the acceptable values are f1.2, f1.4, f1.8, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32.

now when i ask the user to enter an aperture value they will enter a value such as f1.2.
how to i store the number in that. and how do i check again the acceptable values?


i was told to look at getting the aperture as two parts (although as one single string e.g.
f2.8) - the initial character, and then a floating point number.

although i dont understand what he was talking about.

The format string in scanf will let you specify characters that shouldn't appear in the variable you're assiging to.

Code:

---

scanf ("%dcm", &number_of_centimetres);

---

As an example. If you think about it, you don't need to store the 'f' at all, have scanf throw it away for you and store only the float part.

QuantumPete

Well, one question is of course: Do you NEED to store the value as a floating point value, or just as a string (as suggested by others). The only good reason to store the aperture as a float is if you need to calculate on it, otherwise just store it as a string - then you could have a list of valid values and compare your string with the "list of valid".

If you are going to use the aperture as floating point (either because your teacher requests is, or because you need to have values you can calculate with), then you could have a list of float values that are valid. Bear in mind here that floating point values are not precise, so comparisons should be done by using a differentiating function, such as absolute difference between input and table value is less than 0.001 or some such).

--
Mats

i have to later use this value to calculate exposure time,
so yes i will have to have use the aperture as a floating point number.

could you give me an idea as what the code would like like.
but im really struggling with how to start this off.
i know what i have to do,
but to right this in C im not sure.

i dont need you to write it for me,
just kinda give me an idea of what the code would look like.
pseudo code will help.

if i limit the floating to say 1 decimal place will this then store the right value?


just need someone to bounce ideas off as i dont know any1 in my class.

thanks.

Quote:

---

Originally Posted by k4k45hi

i have to later use this value to calculate exposure time,
so yes i will have to have use the aperture as a floating point number.

could you give me an idea as what the code would like like.
but im really struggling with how to start this off.
i know what i have to do,
but to right this in C im not sure.

i dont need you to write it for me,
just kinda give me an idea of what the code would look like.
pseudo code will help.

if i limit the floating to say 1 decimal place will this then store the right value?


just need someone to bounce ideas off as i dont know any1 in my class.

thanks.

---

It would probably be a good idea if you try to get friendly with some of your class-mates...

When you say "limit floating to 1 decimal point", I presume you are referring to the format when using for example printf. This has NOTHING to do with the internal representation of a floating point number. There is no way to change that (other than modifying the design of the processor your are using, which isn't an option). The problem with floating point comparisons is that the number itself is an approximation. If you have the value 1.0, it's quite possible that the ACTUAL value, at least after some calculations[1], is actually 0.9999999999999 or 1.0000000001375 or some such. If you then compare that value EXACTLY with 1.0, then it's not equal. So the solution is to use a calculation where you compare the difference (or the quotient) of two values, rather than an "equal" or "not equal" comparison.

One famous "problem with floating point" is 0.7 - it can not be described precisely in floating point, it generates an infinitely repeating patters (just like 1/3 gives 0.333333...), 0.7 becoems 0.6999...

As to some ideas of how you should solve your problem: Use an array of values, and then verify that the value entered by the user is one of the values in your array.

[1] You may then say that "I just read the value in, not using any calculations on it", but the fact of the matter is that scanf() and similar functions use calculations to form the number, so yes, the number is CALCULATED if it's an input.

--
Mats

this is what i now have.
although the aperture does not work,
it comes with a segmentation fault.
is what im doing correct or am i on the wrong track.
atm im not testing the aperture,
just getting the input.

Code:

---


#include <stdio.h>
#include <string.h>

int main(int argc, char ** argv)


{
  // Mainline Variable Declarations
  FILE * output = stdout;
  FILE * input = stdin;

  float  exposuretime;
  float aperture;
  char aperturef;

 fprintf(output,"please enter exposure time: ");
  fscanf(input,"%f",&exposuretime);


  fprintf(output,"please enter aperture value: ");
  fscanf(input,"%f",&aperture);
  fscanf(input,"%s",&aperturef);


  fprintf(output,"the exposure time is: %f\n ",exposuretime);
  fprintf(output,"the aperture value is %s%f\n ",aperturef, aperture);

}

---

Quote:

---

Originally Posted by k4k45hi

this is what i now have.
although the aperture does not work,
it comes with a segmentation fault.
is what im doing correct or am i on the wrong track.
atm im not testing the aperture,
just getting the input.

Code:

---

...
  float  exposuretime;
  float aperture;
  char aperturef;
...
  fscanf(input,"%s",&aperturef);
...
  fprintf(output,"the aperture value is %s%f\n ",aperturef, aperture);

}

---

---

Reading a string into a single char will certainly overwrite some other data. Also, using fscanf() is dangerous way to read strings if too much input is given.

printing a single character as a string is also bound to fail sooner or later.

--
Mats

Code:

---

char aperturef;
...
fscanf(input,"%s",&aperturef);

---

You're trying to put a string into a char! That won't work, either declare a char array that is big enough to hold your string or malloc some memory for it.

QuantumPete

P.S. What matsp said...

i dont really understand.

gah. ive never been able to do programming.

Your variable aperturef is a char. That can hold ONE character. %s when used in scanf will absolutely read in AT LEAST two characters, one being what you typed, the second being a zero to indicate the end of the string. So the next location in memory after aperturef will be set to zero. If there's some meaningfull data in that location, it will be overwritten by this zero.

The point about printing it is related to the same - printf() will see %s as an indication that the argument is a pointer to char, where there is zero or more characters followed by a zero-character. E.g. "Hello" would be (( 'H', 'e', 'l', 'l', 'o', 0 )). If you try to do this with a char only, printf will continue along until it finds a zero - whcih if you are not lucky, could be severa dozen or hundreds of bytes of memory! If you are "really unlucky", it runs to a point where there is no valid memory any longer, and the application crashes!

--
Mats

ok.

thankyou. that actually makes sense.
so in this case. do i need to change my input method of %s.
or should i change my char to something that can hold more characters.

Quote:

---

Originally Posted by k4k45hi

ok.

thankyou. that actually makes sense.
so in this case. do i need to change my input method of %s.
or should i change my char to something that can hold more characters.

---

Yes, one of those two would work. You can choose either.

By the way, it looks like your code expects 1.4f rather than f1.4 - not sure that's what you meant to do.

--
Mats

i think i will go with the changing %s.

now what can i change this to to make it work.
and ive changed the inputs around so that aperturef is first.

Quote:

---

Originally Posted by k4k45hi

i think i will go with the changing %s.

now what can i change this to to make it work.
and ive changed the inputs around so that aperturef is first.

---

Try googling something like "format specifiers scanf" perhaps?

One of the important parts of learning to program is "how to find information about what you are doing" - there won't always be someone else to ask.

--
Mats

ok well,
i had done that while waiting for a reply and had replaced the %s with a %c.

so the program no longer comes up with a segmentation fault but instead reads back 0.000000. i will give it a shot and see if i can get it on my own.

and let you know how i go.

thanks for all your help mate.

why is this code returning 0.000000.
ive tried everything i could see, but nothing fixed it.

Code:

---


  float aperture;
  char aperturef;

  fprintf(output,"please enter aperture value: ");
  fscanf(input,"%c%f",&aperturef,&aperture);

  fprintf(output,"the aperture value is %c%f\n ",aperturef,aperture);

---

works for me...

What exactly is the problem? I type in:
f1.2
and that's what I get out as well, that's what you want, no?

QuantumPete

must mean the rest of the code must be interfering with it.

heres the whole thing.

Code:

---


#include <stdio.h>
#include <string.h>

int main(int argc, char ** argv)


{
  // Mainline Variable Declarations
  FILE * output = stdout;
  FILE * input = stdin;

  float  exposuretime;
  float aperture;
  char  aperturef;

  fprintf(output,"please enter exposure time: ");
  fscanf(input,"%f",&exposuretime);


  fprintf(output,"please enter aperture value: ");
  fscanf(input,"%c%f",&aperturef,&aperture);

  fprintf(output,"the exposure time is: %f\n ",exposuretime);
  fprintf(output,"the aperture value is %c%f\n ",aperture,aperturef);

}

---

Code:

---

fprintf(output,"the aperture value is %c%f\n ",aperture,aperturef);

---

You have aperture and aperturef the wrong way round!

You may want to check the return result from fscanf(), e.g.

Code:

---

  int res;
  ....
  res = fscanf(...);
  if (res != number_of_things_wanted) {
      printf("error...");
  }

---

For example, fscanf(stdin, "%d %d", &i1, &i2) woould return 2 on successfull read of two integers.

--
Mats

hmm.

ive never used return result

well ive changed aperture with aperturef. but didnt make a difference

it works if i dont type the f.

so something is wrong with the character.

it works if i dont type the f.
hmm.

Most functions return something to indicate what the function did, if it "went ok or not", or some other information that may or may not be important to you. In this case, I'm suspecting that fscanf does it's usual trick of "getting stuck".

scanf is famous for being obnoxious about "rubbish in the input stream". For example, if we have

Code:

---

int i1, i2;
scanf("%d", &i1);
...
scanf("%d", &i2);
...

---

Then someone enters (perhaps by mistake):
1a
2
...
i1 will have the value 1, and the next thing in the input buffer is a. So scanf stops here, and doesn't consume any more of the input, then next scanf fails to read i2, because a is not a digit, and thus it skips out.

There's a FAQ entry for this, if you want further info.

--
Mats

just thinking.
i dont really understand the line

Code:

---

int main(int argc, char ** argv)

---

could this have anything to do with it?

*Only* for the final printing! The scanf was correct.
Btw, you should rethink your variable naming convention, to me, the 'f' at the end of aperture would indicate that it's the float, not the char! If you rename them to something sensible, that might go a long way towards finding the bug ;-)

QuantumPete

Quote:

---

Originally Posted by k4k45hi

just thinking.
i dont really understand the line

Code:

---

int main(int argc, char ** argv)

---

could this have anything to do with it?

---

That is the arguments to your program. Most likely, you can ignore all of it.

--
Mats

Code:

---

    int main(int argc, char ** argv)

---

Er, no, that one's very important. It's basically the entry point for your program (Hence the 'main' part). As you may know from Unix, you can pass arguments to programs (if you haven't covered this yet, you will). The 'argc' gives you a count of how many arguments were passed and the 'argv' gives you pointers to string of the actual arguments passed. You definitly don't want to play around with that.

QuantumPete

What matsp means is that, for this program, having the command line parameters is not necessary and thus they can be ignored since command line arguments are not used.

I know ;-) I took too long to post my response. I was actually referring to k4k45hi's question.

well it still isnt working.

ive tried for hours now,
and cannot debug this.

it prints out the correct exposure time,
but prints out 0.0000 for aperture.

can anyone see what is the problem.

Can you repost your program? Exactly what you have right now, I'll take a look.

QuantumPete

Quote:

---

Originally Posted by k4k45hi

well it still isnt working.

ive tried for hours now,
and cannot debug this.

it prints out the correct exposure time,
but prints out 0.0000 for aperture.

can anyone see what is the problem.

---

Do you check the return value (result) of fscanf() like I suggested. Does it return the right value(s)?

--
Mats

hey mate.

finally figured out the res thing.
and as soon as i include that in the program the program prints out the correct value.

i dont get it. but hey.

well as my program now has to check to see if the values entered are value i will change stuff around and see what happens.

is it possible to use an if statement to check that focus,aperture = the appropriate values which are f1.2, f1.4, f1.8, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32.

i tried it with

Code:

---


  res = fscanf(input,"%c%f",&focus,&aperture);

  if (focus,aperture = f1.2)
  {
  fprintf(output,"error");
  }

---

Remember that floats are approximates, but that only *should* matter if you do any calculations on it.

writing a function, or even a macro to check if it's aperture is good, for example

Code:

---

int isValid(char focus, float app)
{
    int i, a;
    char validFocuses[] = {'f'};
    float validApp[] = {1.2f, 1.4f, 1.8f, 2.0f, 2.8f, 4.0f, 5.6f, 8.0f, 11.0f, 16.0f, 22.0f, 32.0f};

    /* check if the focus is valid for each app */
    for(i = 0; i < (sizeof(validFocuses) / sizeof(validFocuses[0])); i++)
    {
        for(a = 0; a < (sizeof(validApp) / sizeof(validApp[0])); a++)
        {
            if(focus == validFocuses[i] && app == validApp[a])
                return 1;      /* valid */
        }
    }
    return 0;  /* failed, not valid */
}

---

Then you can simply check,

Code:

---

/* ... */
res = fscanf(input, "%c%f", &focus,&aperture);

if(IsValid(focus, aperture) == 0)
    fprintf(output,"error");

/* ... */

---

Remember that '=' is the assignment operator, '==' means "Is Equal to" (use in conditions).

Just as a note, the f at the end of 1.2f is to indicate that the number is a float (rather than the double floating point format, whcih can't be distinguished by the compiler simply from the digits themselves) - so it has nothing to do with the "f-value" that you are working with.

--
Mats

Haha so many people here are from the EP100 class LOL

Quote:

---

Originally Posted by zacs7

Remember that floats are approximates, but that only *should* matter if you do any calculations on it.

writing a function, or even a macro to check if it's aperture is good, for example

Code:

---

int isValid(char focus, float app)
{
    int i, a;
    char validFocuses[] = {'f'};
    float validApp[] = {1.2f, 1.4f, 1.8f, 2.0f, 2.8f, 4.0f, 5.6f, 8.0f, 11.0f, 16.0f, 22.0f, 32.0f};

    /* check if the focus is valid for each app */
    for(i = 0; i < (sizeof(validFocuses) / sizeof(validFocuses[0])); i++)
    {
        for(a = 0; a < (sizeof(validApp) / sizeof(validApp[0])); a++)
        {
            if(focus == validFocuses[i] && app == validApp[a])
                return 1;      /* valid */
        }
    }
    return 0;  /* failed, not valid */
}

---

Then you can simply check,

Code:

---

/* ... */
res = fscanf(input, "%c%f", &focus,&aperture);

if(IsValid(focus, aperture) == 0)
    fprintf(output,"error");

/* ... */

---

Remember that '=' is the assignment operator, '==' means "Is Equal to" (use in conditions).

---

hey mate.
i dont understand the bit highlighted

my code just prints out errorerrorerrorerror, even if i enter the correct value.

Code:

---

for (i=0;i<(sizeof(validfocus) / sizeof(validfocus[0]));i++)
  {
  for (j=0;j<(sizeof(validaperture) / sizeof(validaperture[0]));j++)
  {
    if ((focus == validfocus[i])&&(aperture == validaperture[j]))
    {
    fprintf(output,"the aperture value is: %c%f\n ",focus,aperture);
    }
    else
    {
    fprintf(output,"error");
    }
  }
  }

---

(sizeof(validFocuses) / sizeof(validFocuses[0])) = The size of the focus array, I wasn't sure you would need more than 1 focus value, ie other than 'f' - so I put it in an array anyway.

It Prints error because you're checking it every iteration, leave it in a function like I demonstrated...

ok im confused.
for now i just want the program to check to see what is valid
and if they are valid print the value if not print error.

i know later i can return 1 when i need to go back to the menu.
but atm i dont have a menu im just creating the test code.

Quote:

---

Originally Posted by k4k45hi

ok im confused.
for now i just want the program to check to see what is valid
and if they are valid print the value if not print error.

i know later i can return 1 when i need to go back to the menu.
but atm i dont have a menu im just creating the test code.

---

You obviously only have one valid value (at any given time), so there are a few options:
- use a function as zacs7 suggests, and let the loop be in the function.
- use two loops like you've done, but use a variable to say "there's a valid value", which is set initially to "not valid", and when you find a value that is valid, set it to one.

By the way, the way your loop is designed right now, it tests both values together in one test, which means that you need to test EVERY permutation (n * m, where n is number of shutter speeds and m is number of apertures). But if aperture is in the valid set, and shutter speed is in the valid set, then by definition it is a valid combination. So you could do two loops, one after the other, rather than one inside the other, and only have to do n + m loops. The bigger the n and m values are, the bigger the difference would be. Consider n and m being 10 each, you do 100 loops in the first model, and 20 in the second model. If there's n=100, m=200, then the model one does 20000 tests, and model 2 does 300 tests - that is a BIG difference. [Of course, it doesn't make much difference here, it's just good practice to do not put loops inside each other when they don't need to be].

--
Mats

like this (although this doesnt work, just prints out random large number)

Code:

---

for (i=0;i<(sizeof(validfocus) / sizeof(validfocus[0]));i++)
  {
  for (j=0;j<(sizeof(validaperture) / sizeof(validaperture[0]));j++)
  {
    if ((focus == validfocus[i])&&(aperture == validaperture[j]))
    {
    // fprintf(output,"the aperture value is: %c%f\n ",focus,aperture);
    valid = 1;
    }
  }
  }
  if (valid = 1)
  {
  fprintf(output,"the aperture value is: %c%f\n ",focus,aperture);
  }
  else if (valid =0)
  {
  fprintf(output,"error");
  }
}

---

Quote:

---

Originally Posted by k4k45hi

like this (although this doesnt work, just prints out random large number)

Code:

---

for (i=0;i<(sizeof(validfocus) / sizeof(validfocus[0]));i++)
  {
  for (j=0;j<(sizeof(validaperture) / sizeof(validaperture[0]));j++)
  {
    if ((focus == validfocus[i])&&(aperture == validaperture[j]))
    {
    // fprintf(output,"the aperture value is: %c%f\n ",focus,aperture);
    valid = 1;
    }
  }
  }
  if (valid = 1)
This sets valid to one, then tests if it's true which it always is - you want double = signs to test for equality.
  {
  fprintf(output,"the aperture value is: %c%f\n ",focus,aperture);
  }
  else if (valid =0)
This sets valid to zero, then tests if it's true which it is never - and since this is the only other alternative, why use a second if - assuming valid is set to zero, the above code just sets to one possible other value, 1, which the above code tests for, so if we get past that valid should be zero and nothing else [if it is something else, then it's because of some other bug!]
  {
  fprintf(output,"error");
  }
}

---

---

See comments in red above.

--
Mats

oh yeh. my bad.

how come nothing prints,
it still prints the exposure which the printf statement is located before the for loops.

but for the aperture, it doesnt print anything out, not even an error.

can anyone explain.

Just a little note: If you want to help yourself to avoid the "single equal sign error", you could reverse the comparison:

Code:

---

  // The following compiles.
  if( 1 == valid )  ...
  // This gives an error - because you are trying to assign a value to the constant 1, which is forbidden.
  if (1 = valid ) ...

---

At first, it looks a bit different, but if you consistenly use this form, then you'll avoid those nasty errors that happen when you assign instead of compare. I don't use this style, but I've seen it many times, and if you are starting out, it's perhaps a good habit to start with.

--
Mats

Quote:

---

Originally Posted by k4k45hi

oh yeh. my bad.

how come nothing prints,
it still prints the exposure which the printf statement is located before the for loops.

but for the aperture, it doesnt print anything out, not even an error.

can anyone explain.

---

this is whats happening after i change it to ==.
before it was printing random large numbers.

Could you post the code, please (the interesting parts, not the whole lot).

--
Mats

Code:

---


  int i;
  int j;
  float  exposuretime;
  float aperture;
  char focus;
  int res;
  char validfocus[] = {"f"};
  float validaperture[] = {1.2f,1.4f,1.8f,2.0f,2.8f,4.0f,5.6f,8.0f,11.0f,16.0f,22.0f,32.0f};
  int valid = 0;


  for (i=0;i<(sizeof(validfocus) / sizeof(validfocus[0]));i++)
  {
  for (j=0;j<(sizeof(validaperture) / sizeof(validaperture[0]));j++)
  {
    if ((focus == validfocus[i])&&(aperture == validaperture[j]))
    {
    // fprintf(output,"the aperture value is: %c%f\n ",focus,aperture);
    valid = 1;
    }
  }
  }
  if (valid == 1)
  {
  fprintf(output,"the aperture value is: %c%f\n ",focus,aperture);
  }
  else if (valid ==0)
  {
  fprintf(output,"error");
  }
}

---

Code:

---

  char validfocus[] = {"f"};
  ...
  if ((focus == validfocus[i])&&(aperture == validaperture[j]))

---

I don't think that's what you want. I'm guessing there is only one char that is 'valid', so do this instead:

Code:

---

const char validfocus = 'f';
...
if ((validfocus == focus) && (aperture == validaperture[j]))

---

and then lose the outer for loop.

QuantumPete

and remove the for focus for loop?

nevermind.
i did it anyway.

still wont print anything out.

gahhh. getting annoyed now.

I don't see anything wrong in that code. Try to add some debug output in various places (e.g. uncomment your printf when you set valid = 1 to see if it gets there.

You may want to add a "\n" to the end of "error" to make it look better - this shouldn't make any difference to the execution of the code.

--
Mats

well i tried this

Code:

---

for (j=0;j<(sizeof(validaperture) / sizeof(validaperture[0]));j++)
  {
    if ((validfocus == focus)&&(aperture == validaperture[j]))
    {
    fprintf(output,"the aperture value is correct");
    valid = 1;
    }
  }

---

but it still didnt print out anything.
what does this mean.

it now semi works.
it compiles.
and when i type any of the correct values it will print the correct value.
and if the number is not correct it will print and error
buut if it does not recieve the 'f' it will sit for about 10min without doing anything.
by then i got frustrated of waiting and suspending it.


if you want the full code i can send it to you,
but i cannot afford for others in my class to steel the full code as i can be done for plagerism.

im so close now.

just quiet get it.

Are you checking to see if you have the right number of values back from fscanf(), like I suggested on Friday?

--
Mats

yeh ive tried it.

its even in my code atm.
but for some reason even if i dont enter two values it wont work.

Quote:

---

Originally Posted by k4k45hi

yeh ive tried it.

its even in my code atm.
but for some reason even if i dont enter two values it wont work.

---

No, what I'm trying to make you do is get an error message if there's the wrong number of things for fscanf to operate correctly.

Note also that fscanf is prone to "messing up" your input. Perhaps a better approach is to read using fgets() and using the result of fgets() to feed into sscanf() - the problem here is that if fscanf() is fed "bad stuff", then it willl just sit there refusing to get any data in at all. Say for example you are trying to read with scanf("%d"), and the current input is "a", then it will not progress past the a EVER! It's stuck.

--
Mats

we dont use fgets.
i dont know if im allowed to use it. only what ive been tought.

would fflush do anything?

Quote:

---

Originally Posted by k4k45hi

we dont use fgets.
i dont know if im allowed to use it. only what ive been tought.

would fflush do anything?

---

fflush is invalid on input streams, so no.

If they are telling you to use fscanf(), then you have to live with that. But you need to make sure that your input is exactly where you're expecting it.

Is it a real requirement to read in "f1.2" rather than "1.2" for teh aperture? It may simplify things a lot if you don't attempt to read the "f" part (and if you do, try to make sure your code accepts both "f" and "F").

--
Mats

yes they want the f. which makes it so much harder. ive got it so close.

this sucks.

Quote:

---

Originally Posted by k4k45hi

yes they want the f. which makes it so much harder. ive got it so close.

this sucks.

---

Are you allowed to use sscanf()? If so, you could use something like:

Code:

---

char str[100];
...

fscanf(f, "%s", str);
if (tolower(str[0]) == 'f' && isdigit(str[1])) {
  sscanf(&str[1], "%f", &aperture);
  ...
}
...

---

Note that as opposed to fgets(), any version of scanf is not resistant to "buffer overflow". And strange things may happen if someone enteres "f1f" or some such.

--
Mats

i want to know why res doesnt kick in when it should.

ive even tried 1.2f.

that freezes to.

f1f but will print the error message.

Quote:

---

Originally Posted by k4k45hi

i want to know why res doesnt kick in when it should.

---

Huh?

--
Mats

let's see the part where you use scanf again

QuantumPete

http://pastebin.com/d2d9d78f4

Did you mean to have

Code:

---

  fscanf(input,"%c%f",&focus,&aperture);

  res = fscanf(input,"%c%f",&focus,&aperture);

---

this twice?

Also, float validaperture[] = {1.2,1.4,1.8,2.0,2.8,4.0,5.6,8.0,11.0,16.0,22.0,32 .0f};

All of those values should be 1.2f, 1.4f, etc, not just the last one. And stick a "const " in front of that list, so that compiler understands that you'll never change it.

Code:

---

...
else if (valid ==0)
...

---

As I said earlier, remove the "if (valid == 0)" here, as you've already tested the only other value that "valid" could have in

Code:

---

if (valid == 1)

---

, so ANY other value is by definition zero (because you only have two values ever set on this variable).

--
Mats


--
Mats

input output
exposure 1.2 1.2
aperture f1.2 f1.2

exposure f1.2 res error
aperture f1.2

exposure f1.2 0.0
aperture 1.2 did not enter correct value

exposure 1.2 1.2
aperture f1.2 f1.2

exposure 1.2 freezes
aperture 1.2

exposure 1.2 1.2
aperture c1.2 did not enter correct value

exposure 1.2 1.2
aperture f1.3 did not enter correct value

with the second one the res error shouldnt be effecting the exposure, as i thought it was looking at scanf from the aperture. or does it look at both scanf's ?

for the third one i need an error message if exposure is wrong.
but that still doesnt explain why the error message works for aperture. which is right, but why is it working now.

why does it freeze.

and the last one is right.