Thread: float from a string

What is wrong with this code:

#include <stdio.h>
#include <math.h>

void main()
{
char str[] = "123456789" ;
float f;

f = ( atof( str ) / 100 );
printf(" %f7.2", f);
}

It doesn't give me the desired result of 1234567.89

Please could you explain why this is and how I can achieve it.

one make f a double.

double f;

two,

your format specifier is wrong

printf(" %f7.2", f); should be

printf(" %7.2f", f);

If I use:
double f;

instead of
float f;

how can I convert the string instead of atof();

T

>how can I convert the string instead of atof();

i don't get you meaning atof() will work with doubles too, since all your after is the return?

You need to cast the result of atof to a float or use a double variable. Your compiler should give you a warning if you don't about converting double to float. void main is not right, it's possible that the runtime startup code might not be able to call main properly if it isn't defined with a very specific tag, that tag is

int main()
or
int main( int argc, char *argv[] )

You can also use just

main()
or
main( int argc, char *argv[] )

because if you don't give any return value at all C will assume you meant to use int. It's a neat trick if that kind of thing appeals to you.

You also don't want to use atof because if the string you pass to it is too big for a double then anything can happen. And atof is declared in stdlib.h, not math.h. It may be in math.h on your compiler, but that isn't a standard practice.

Code:

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

int main()
{
	char str[] = "123456789";
	float f;
	
	f = (float)( strtod( str, NULL ) / 100 );
	printf("%7.2f\n", f);
	return 0;
}

Bebop