C Program to Calculate the Average of 3 Numbers using Function

In this article, we will write a C program to calculate the average of 3 numbers using function. The program takes three numbers from the user as input, calculates their average and prints the result on the output window.

Sample Example:

Enter three numbers: 10 20 30
Average of 10, 20 and 30 is: 20.000000

Enter three numbers: 5 2 7
Average of 5, 2 and 7 is: 4.666667

To calculate the average of three numbers using a user-defined function, we have to create a function that takes the three numbers as argument, calculates their average and returns the result.

As the average of three numbers can be an integer or a float value, therefore, we will keep the return type of the function a float which will take care of both integer and decimal point numbers. A float value is nothing but a decimal point value.

See implementation in the following program:

// C program to find the average
// of three numbers using a function

#include <stdio.h>

// Function declaration
float average(int, int, int);

int main() {

    int num1, num2, num3;
    float avg;
    printf("Enter three numbers: ");
    scanf("%d %d %d", &num1, &num2, &num3);
    // Get average using average() function
    avg = average(num1, num2, num3);
    printf("Average of %d, %d and %d is: %f", num1, num2, num3, avg);    
    return 0;


// Function to calculate average of three numbers
float average(int x, int y, int z){
	float avg;
	avg = (x + y + z)/3.0;
	return avg;


Enter three numbers: 20 30 40
Average of 20, 30 and 40 is: 30.000000

Enter three numbers: 10 11 11
Average of 10, 11 and 11 is: 10.666667

Program Explanation:

  • The program begins with the declaration of a function called average(), which takes three integer parameters (x, y, and z) and returns a floating-point value (avg).
  • This function is declared before the main() function to inform the compiler about its existence.
  • Variables num1, num2, and num3 are used to store user-input numbers and a floating-point variable avg to store the calculated average.
  • To calculate the average of the three input numbers, the average() function is called inside the main() function with the values of num1, num2, and num3 as arguments.
  • The result is stored in the avg variable.
  • Finally, the program uses printf() to display the calculated average along with the input values.

That’s all for this article. Thanks for reading!


  • Manoj Kumar

    Hi, My name is Manoj Kumar. I am a full-stack developer with a passion for creating robust and efficient web applications. I have hands-on experience with a diverse set of technologies, including but not limited to HTML, CSS, JavaScript, TypeScript, Angular, Node.js, Express, React, and MongoDB.