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In this tutorial, you will learn how to write a program in C to print sum of all even numbers between 1 to n using while loop. Here, we will go through examples, algorithms, logic, and program explanation for your better understanding of this problem.

Required Knowledge

• C Programming Basics
• C Programming Operators
• C printf and Scanf
• While loop in C

Problem Statement

You have to Write a C program that takes a positive integer ‘n’ as input from the users. After taking the input, the program should print the sum of all even numbers between 1 and n using a while loop. The program provides a solution to find the sum of even numbers using a while loop in the C programming language. You can refer to the below example to understand what we have to achieve.

Example

Input:
Enter the value of n: 10

Output:
The sum of even numbers between 1 and 10 is: 20

In the above example, you can see that the user has given input Integer 10. From 1 to 10, there are four variables that are even numbers 2, 4, 6, and 8. The sum of these even numbers is 20, so the output will be 20.

Algorithm

1. Start the program.
2. Declare the variables: n to store the input value, num to represent the current number, and sum to store the sum of even numbers.
3. Read the value of n from the user.
4. Initialize num to 1 and sum to 0.
5. Enter the while loop with the condition num < n.
   • Check if the current number num is even using the modulo operator (num % 2 == 0).
   • If it is even, add num to sum.
   • Increment num by 1.
6. Exit the while loop.
7. Print the sum of even numbers as: “The sum of even numbers between 1 and n is: sum”.
8. End the program.

Logic used to solve this problem

• Declare a variable to hold the input number.
• Prompt the user to enter a number.
• Read and store the entered number in the variable.
• Initialize a variable to hold the sum of even numbers and set it to 0.
• Initialize a num variable to 1.
• Use a while loop that runs as long as the num is less than to the given number (n).
• Inside the loop, check if the num is an even number using the modulo (%) operator.
• If the num is even, add it to the sum variable.
• Increment the num by 1 in each iteration.
• Continue the loop until the num reaches the given number (n).
• Print the sum of even numbers.
• Finish the program.

Program to print the sum of all even numbers between 1 to n

#include <stdio.h>
int main() {
    int n, num = 1, sum = 0;
    printf("Enter the value of n: ");
    scanf("%d", &n);
    while (num < n) {
        if (num % 2 == 0) {
            sum += num;
        }
        num++;
    }
    printf("The sum of even numbers between 1 and %d is: %d\n", n, sum);
    return 0;
}

Output

Enter the value of n: 12
The sum of even numbers between 1 and 12 is: 30

Program Explanation

• The program takes input for the value of n from the user.
• It initializes a variable num to 2, which represents the first even number to be considered for summation.
• It also initializes a variable sum to 0, which will hold the running sum of even numbers.
• The program enters a while loop with the condition num < n to iterate through numbers from 2 to n.
• Inside the while loop, it checks if num is an even number.
• If num is even, it adds the value of num to sum.
• It then increments the value num by 2 since the next even number will be 2 greater than the current one.
• The loop continues until num exceeds the value of n.
• Once the while loop is complete, the program prints the value of, which represents the sum of all even numbers between 1 and n.
• Here n is not inclusive in the addition.
• The program ends.

Conclusion

The C program successfully calculates and prints the sum of all even numbers between 1 and the given input n using a while loop. By iterating through the numbers and checking their divisibility by 2, it identifies the even numbers, calculates their sum, and displays the result on the screen. I hope you liked our tutorial. Please do share.