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What can I add to my function that will make sure only numerical input is added? This is not for homework.
Thanks :cool:Code:float num_check (float num_entd)
{
while((num_entd>1000) || (num_entd<0))
{
printf("Please enter a valid weight between 0 and 1000 lbs\n");
scanf("%f", &num_entd);
}
return num_entd;
}
Read a line using fgets()
Then parse the line using sscanf or strtod
PS
There is no need to pass num_entd as a parameter. Just make it a local, and return it.
Check the return value of scanf and handle the three cases appropriately.
scanf(3) - Linux manual page
I am sending in a float value though. Are you saying I can just get rid of the (float num_entd) even though I'm sending in a float?Quote:
Originally Posted by Salem
Unfortunately, I don't yet know any of those commands :(
How about this?Quote:
Originally Posted by Barney McGrew
Code:float num_check (int tester, float num_entd)
{
while((num_entd>1000) || (num_entd<0) || tester=0)
{
printf("Please enter a valid weight between 0 and 1000 lbs\n");
tester=scanf("%f", &num_entd);
}
return num_entd;
}
Ignore my wrong equals sign. tester==0
You have "... || tester=0", which assigns 0 to tester rather than checking whether tester is 0. You should be using ==. [edit] Fixed, I see. [/edit]
How about something like this?
Could think about using a do-while loop as well.Code:while(scanf("%f", &value) != 1 || value < 0 || value > 1000) {
printf("Please try again.\n");
}
Or something.Code:int read;
do {
// ...
read = scanf("%f", &value);
} while(read != 1 || value < 0 || value > 1000);
[edit] Why are you passing in the variables as arguments? Then the calling function has to provide values. Declare the variables locally.
[/edit]Code:void func() {
int local_x;
float local_y;
// ...
}
> I am sending in a float value though. Are you saying I can just get rid of the (float num_entd) even though I'm sending in a float?
Why call the function with
result = num_check (123.456);
when that number has nothing to do with the result you get - it will be overwritten when you read something from the user.
> Unfortunately, I don't yet know any of those commands
Here's a tip - every time you see a new function, your first instinct should be to either use google, or read your manual pages.
Saying "I don't know what foo does" everytime will be just frustrating for everyone involved.
The reason for using fgets() to read a line, is simply that it's a nice neat way of keeping the input stream consistent.
Because simple code like this runs into all sorts of trouble should scanf return zero (indicating that no conversion took place).Code:int read;
do {
// ...
read = scanf("%f", &value);
} while(read != 1 || value < 0 || value > 1000);
scanf does NOT purge the input stream in any way, when presented with invalid data.
So you have to resort to hackery like this -> FAQ > Flush the input buffer - Cprogramming.com
That only handles the case where scanf returns 0. You need to check the case where it returns EOF (to indicate that there's no more data on stdin, or an error has occurred.) Since you've chosen an interactive design for your program, the following should be sufficient for your purposes:Quote:
Originally Posted by gratiafide
Using that function is fairly straightforward. It returns EOF if there's no more input, 0 if a value was successfully converted and stored in 'to', and 1 if there was an error on the line.Code:#include <ctype.h>
#include <stdio.h>
static int discardline(FILE *stream)
{
int c;
while ((c = getc(stream)) != '\n' && c != EOF)
;
return c;
}
int readf(float *to, float min, float max)
{
const char *invalid = "invalid character: %c";
int r;
if ((r = scanf("%f", to)) == EOF)
return EOF;
if (!r) {
warn(invalid, getchar());
return discardline(stdin) == EOF ? EOF : 1;
}
while ((r = getchar()) != EOF && r != '\n')
if (!isspace(r)) {
warn(invalid, r);
return discardline(stdin) == EOF ? EOF : 1;
}
if (*to < min) {
warn("%f < %f", *to, min);
return 1;
}
if (*to > max) {
warn("%f > %f", *to, max);
return 1;
}
return 0;
}
Okay that's nice code but I don't know that it's simple to use. The reason I was trying to post simple code is because given the OP's passing in of variables that should be local, I thought they would need some intermediate code before seeing complete code to be able to understand what's going on.
Anyway, basically you have a few errors that can happen. The user can enter non-numeric values, or the input stream can reach end-of-file. If you're reading data with scanf("%f") and you see non-numeric values, you have to skip over them before calling scanf() again (otherwise it will continue to fail); if you are reading input line-by-line then you can simply grab another line. In addition, you're checking whether the values entered are within a specific range.
How many of these errors you want to handle is up to you. You've already seen Barney McGrew's example using scanf() and getchar() to do the character-by-character case. If you want to try reading lines you can do something like
On end of file, you might exit the program or substitute some kind of default value. Or as in the previous code, return an error code and let the calling function handle it.Code:char line[BUFSIZ];
float value;
while(fgets(line, sizeof line, stdin)) {
if(sscanf(line, "%f", &value) == 1) {
// found a float. Could also check for junk characters after the value if you wanted
return value;
}
// nothing float-like on this line, grab another line
}
// end of file
I really appreciate all the effort put into these posts. I keep thinking there is an easy way to do these things and it usually seems it is not so easy. It will take me a while to digest all this but thanks so much!