Header File 

math.h  

Category 

Math Routines, Inline Routines 

Prototype 

double cos(double x); 

long double cosl(long double x); 

Description 

Calculates the cosine of a value. 

cos computes the cosine of the input value. The angle is specified in radians. 

cosl is the long double version; it takes a long double argument and returns a long double result. 

Return Value 

cos of a real argument returns a value in the range -1 to 1. Error handling for these functions can be modified through _matherr (or _matherrl). 

Example  

#include <stdio.h>
#include <math.h>
int main(void)
{
   double result;
   double x = 0.5;
   result = cos(x);
   printf("The cosine of %lf is %lf\n", x, result);
   return 0;
}

Portability