Header File 

math.h  

Category 

Math Routines 

Prototype 

double fabs(double x); 

long double fabsl(long double x); 

Description 

Returns the absolute value of a floating-point number. 

fabs calculates the absolute value of x, a double. fabsl is the long double version; it takes a long double argument and returns a long double result. 

Return Value 

fabs and fabsl return the absolute value of x. 

Example  

#include <stdio.h>
#include <math.h>
int main(void)
{
   float  number = -1234.0;
  
   printf("number: %f  absolute value: %f\n", number, fabs(number));
   return 0;
}

Portability