How to Find Area of a Circle with Diameter in C Program | Functions

How to find area of a circle with diameter in C program.

In this article, you will learn how to find area of a circle with diameter in C program.

Example

You should have knowledge of the following topics in c programming to understand this program:

• C main() function
• C printf() function
• C math.h library

Standard Formula

Where

In this article, we used three ways to solve this problem

• By using the default value of PI = 3.14
• Second, by using the M_PI constant
• By using the Functions

1. By using the default value of PI = 3.14

// How to Find Area of a Circle with Diameter in C Program using PI=3.14
#include <stdio.h>

int main() {
    float r, d = 0, c = 0, a = 0;
    // r = radius, d = diameter, c = circumference, a = area

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

    // Calculation of diameter, circumference, and area
    d = 2 * r;
    c = 2 * 3.14 * r;
    a = 3.14 * (r * r);

    // It will print the final output
    printf("\n");
    printf("Diameter      :: = %f units \n", d);
    printf("Circumference :: = %f units \n", c);
    printf("Area          :: = %f sq. units ", a);
    return 0;
}

Run

Output

Explanation

In this given program, we have taken input 7 from the user then we applied the standard formula to calculate the diameter, circumference, and area.

Then this will return the final outputs 14.000000, 43.959999, and 153.860001 from the above calculation.

2. By using the M_PI constant

// How to Find Area of a Circle with Diameter in C using M_PI Constant
#include <stdio.h>
#include <math.h> // To import M_PI constant

int main() {
    float r, d = 0, c = 0, a = 0;
    // r = radius, d = diameter, c = circumference, a = area

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

    // Calculation of diameter, circumference, and area
    d = 2 * r;
    c = 2 * M_PI * r;
    a = M_PI * (r * r);

    // It will print the final output
    printf("\n");
    printf("Diameter      :: = %f units \n", d);
    printf("Circumference :: = %f units \n", c);
    printf("Area          :: = %f sq. units ", a);
    return 0;
}

Run

How to Find Area of a Circle with Diameter in C using Functions

// How to Find Area of a Circle with Diameter in C using Functions
#include <stdio.h>

// This function will print the diameter, circumference, and area
void CalcCircumferenceArea(float r) {
    float d = 0, c = 0, a = 0;
    // d = diameter, c = circumference, a = area

    // Calculation of diameter, circumference, and area
    d = 2 * r;
    c = 2 * 3.14 * r;
    a = 3.14 * (r * r);

    // It will print the final output
    printf("\n");
    printf("Diameter      :: = %f units \n", d);
    printf("Circumference :: = %f units \n", c);
    printf("Area          :: = %f sq. units ", a);
}

// It's the driver function
int main() {
    float r; // radius of the circle

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

    CalcCircumferenceArea(r);
    return 0;
}

Run

Output

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