double fabs(double);

calculates the absolute number of a given value

compile in linux with: gcc fabs.c -o fabs -lm -Wall

#include <stdio.h> /* including standard library */
//#include <windows.h> /* uncomment this for Windows */
 
#include <math.h> /* including math library */
 
int main ( void ) 
{
double y,x;
x = 4.2422;
y = -3284.2;
printf("the fabs of 4.2422 is %f\n", fabs(x) );
printf("and the fabs of -3284.2 is %f\n ", fabs(y) );
return 0;
}

 output:
 user@host:~$ ./fabs 
 the fabs of 4.2422 is 4.242200
 and the fabs of -3284.2 is 3284.200000