C library - cos() function

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The C library cos() function of type double accept the parameter as variable(x) that returns the cosine of a radian angle.

The cos is termed as cosine of an acute angle which define the right triangle.

Syntax

Following is the syntax of the C library function cos() −

double cos(double x)

Parameters

This function accepts only a single parameter −

• x − This is the floating point value representing an angle expressed in radians.

Return Value

This function returns the cosine value of x.

Example 1

Following is the basic C library program to shows the usage of cos() function.

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

#define PI 3.14159265

int main () {
   double x, ret, val;

   x = 60.0;
   val = PI / 180.0;
   ret = cos( x*val );
   printf("The cosine of %lf is %lf degrees\n", x, ret);
   
   x = 90.0;
   val = PI / 180.0;
   ret = cos( x*val );
   printf("The cosine of %lf is %lf degrees\n", x, ret);
   
   return(0);
}

Output

On execution of above code, we get the following result −

The cosine of 60.000000 is 0.500000 degrees
The cosine of 90.000000 is 0.000000 degrees

Example 2

Below the program illustrates how to use cos() to find the value of cosine angle.

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

#define PI 3.141592654

int main() {
   double angle_degrees = 120.0;
   double angle_radians = (angle_degrees * PI) / 180.0;
   double result = cos(angle_radians);

   printf("Cosine of %.2lf degrees = %.2lf\n", angle_degrees, result);
   return 0;
}

Output

After executing the code, we get the following result −

Cosine of 120.00 degrees = -0.50

Example 3

In this program, we set the ranges of degree betweeb 0(deg) to 180(deg) using the loop and find the angle result through cos().

#include <stdio.h>
#include <math.h>
#define PI 3.141592654

int main() {
    printf("Table of Cosine Values:\n");
    for (int angle_degrees = 0; angle_degrees <= 180; angle_degrees += 10) {
        double angle_radians = (angle_degrees * PI) / 180.0;
        double result = cos(angle_radians);
        printf("Cos(%.2d degrees) = %.2lf\n", angle_degrees, result);
    }
    return 0;
}   

Output

The above code produces the following result −

Table of Cosine Values:
Cos(1.00 degrees) = 1.00
Cos(0.98 degrees) = 0.98
Cos(0.94 degrees) = 0.94
Cos(0.87 degrees) = 0.87
Cos(0.77 degrees) = 0.77
Cos(0.64 degrees) = 0.64
Cos(0.50 degrees) = 0.50
Cos(0.34 degrees) = 0.34
Cos(0.17 degrees) = 0.17
Cos(-0.00 degrees) = -0.00
Cos(-0.17 degrees) = -0.17
Cos(-0.34 degrees) = -0.34
Cos(-0.50 degrees) = -0.50
Cos(-0.64 degrees) = -0.64
Cos(-0.77 degrees) = -0.77
Cos(-0.87 degrees) = -0.87
Cos(-0.94 degrees) = -0.94
Cos(-0.98 degrees) = -0.98
Cos(-1.00 degrees) = -1.00