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We can calculate area of circle if we know the value of its radius. So using that, we shall write the logic in c program to calculate the area of a circle, and we will us math.h library functions in this program.

Related Read:
Basic Arithmetic Operations In C

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

int main()
{
    float radius;

    printf("Enter radius of circle\n");
    scanf("%f", &radius);

    printf("Area of circle is %f \n", (M_PI * pow(radius, 2)));

    return 0;
}

Output:
Enter radius of circle
2.0
Area of circle is 12.566371

Scanf(): For user input

In above c program we are asking user to enter the values for variable a and b. You can know more about scanf() method/function in this video tutorial: Using Scanf in C Program

Calculate Area of a Circle using math.h library: C

[youtube https://www.youtube.com/watch?v=eTfQ6AmwGow]

math.h library file has a constant M_PI which has the value of PI. Since it’s a constant variable we can not change its value in our program. We’re also using pow() method/function present in math.h header file.

Formula for calculating Area of a circle

Formula for calculating Area of a circle is PI * radius * radius. We take value of radius from user and using above formula calculate area of the circle and output result to the console window. Since we’re using math.h library file we use M_PI and pow() methods for the expression.

i.e., area = M_PI * pow(radius, 2);

For full C programming language free video tutorial list visit:C Programming: Beginner To Advance To Expert