atof: string to float

Hi i have just created some code to get the number out of a char array. Now i am not sure if it works. Below is the code:

Code:

---


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

int main(int argc, char ** argv)
{

FILE * output = stdout;
FILE * input = stdin;

char aperture[4];
float apertureNo

        fprintf(output,"Please enter the aperture value (f-stops): "); fflush(output);
        fscanf(input,"%s",&aperture);
       
        apertureNo = atof(aperture);   

        fprintf(output,"Your aperture is \n",aperture);
        fprintf(output,"Your aperture NUMBER is \n",apertureNo);

}

---

Could someone please tell me if it will work.

For example. I enter a1.5

aperture should be: a1.5
apertureNo should be: 1.5
Will the above code do it?

thanks

No that won't work "a1.5" is not a valid double.
Kurt

so how could i get the 1.5 out of it?

Same mistakes as previous posts....

> float apertureNo
This is missing a ;

> char aperture[4];
This isn't large enough to hold a 4-character string AND a \0

> apertureNo = atof(aperture);
If you're confident of the input format, then
apertureNo = atof( &aperture[1] );
will convert from the 2nd character onwards.

you could pass the start of the float tp atof

Code:

---

apertureNo = atof(aperture+1);

---

Checking if aperture[0] really is an 'a' would be a good idea too.
Kurt

missing your format specifiers.

Code:

---

fprintf(output,"Your aperture is %s\n",aperture);
fprintf(output,"Your aperture NUMBER is %f\n",apertureNo);

---

Also, atof() is in <stdlib.h>.

But I'd suggest using strtof() instead, also in <stdlib.h>; it has better error checking. strtof() is just like strtod(), but with floats instead of doubles.

Code:

---

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

int main(int argc, char ** argv)
{

FILE * output = stdout;
FILE * input = stdin;

char aperture[5];
float apertureNo;

        fprintf(output,"Please enter the aperture value (f-stops): "); fflush(output);
        fscanf(input,"%s",&aperture);
       
        apertureNo = atof(&aperture[1]);   

        fprintf(output,"Your aperture is %s\n",aperture);
        fprintf(output,"Your aperture NUMBER %fis \n",apertureNo);

}

---

ok i changed it according to what you guys were saying. Now i use this now: apertureNo = atof(&aperture[1]);

Basically the input will always be in the form 'a1.5' or 'a4'

it will always start with a letter then the rest are numbers.

now will the new code work to get the numbers after the first letter?

Not quite.

Code:

---

fscanf(input,"%s",&aperture);

---

Drop the &, since aperture is a char[].

Code:

---

fprintf(output,"Your aperture NUMBER %fis \n",apertureNo);

---

That will generate output like "Your aperturn NUMBER 1.23is". You probably want

Code:

---

fprintf(output,"Your aperture NUMBER is %f\n",apertureNo);

---

The location of the format specifier like %f is where the number is printed.

[edit] And you're still not including <stdlib.h> for atof(). [/edit]

Code:

---

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

int main(int argc, char ** argv)
{

FILE * output = stdout;
FILE * input = stdin;

char aperture[5];
float apertureNo;

        fprintf(output,"Please enter the aperture value (f-stops): "); fflush(output);
        fscanf(input,"&#37;s",aperture);
       
        apertureNo = atof(&aperture[1]);   

        fprintf(output,"Your aperture is %s\n",aperture);
        fprintf(output,"Your aperture NUMBER is %f \n",apertureNo);
            return(0);

}

---

ok so basically now, will it take the number after the first character?

Not quite. ;)

Code:

---

apertureNo = atof(aperture[1]);

---

You need an & there. :)

Here's why. Both fscanf() and atof() expect a char* string. Since aperture is a string, you can pass it with no adornments to fscanf(). aperturn[1] is a character, so you need to take its address to make it a string as &aperture[1] to pass it to atof(). Or you could just use

Code:

---

apertureNo = atof(aperture + 1);

---

which is the same thing.

I might also suggest one or two other minor changes, like removing the redundant space after the &#37;f, moving the fflush() call onto its own line to make it more readable, and adding a return 0 at the end of main().

ah alright now hopefully its ok. i changed it in post10. seem good. so if i enter a1.4 it will take out the 1.4 and store in apertureNo?

Looks good to me.

By the way, you do know that you can use printf() and scanf() to always use stdout and stdin, right? I guess that you used fprintf() etc so that you can use other streams later, though.

yea thats right, we were taught like that so we what we learn later can be used easier

thanks for the help.

oh by the way: In pseudocode, whats the appropriate language to say get numbers out of char arrat like my case?

Quote:

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oh by the way: In pseudocode, whats the appropriate language to say get numbers out of char arrat like my case?

---

Do you mean, what is the pseudocode for your program? Or what's some pseudocode for extracting digits from array elements? Or pseudocode for searching though a string and getting numbers from it, where the numbers could be anywhere in the string? Or what?

[edit]

Quote:

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yea thats right, we were taught like that so we what we learn later can be used easier

---

Personally, I don't think that's a very good way to do it. I use stdin and stdout all of the time. If I want to use files for input/output, I redirect the input/output of my program, or code it in specially.

And if you really did want to change all occurances of printing to go to a file, you could use freopen().

I realize that this is probably beyond your control, but I just thought I'd comment. [/edit]