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In this tutorial, you will learn how to write a program to print sum of all odd numbers between 1 to n using a while loop in C. Here, we will see examples, algorithms, logics and program explanation for your better understanding in C programming language.

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 should take a positive integer ‘n’ as input. After taking the input it should print the sum of all odd numbers between 1 and n using a while loop. The program provides a solution to find the sum of odd numbers using a while loop in the C programming language. You can refer to the below example to understand better what we have to achieve. The first value and n will be not included in the operation.

Example

Input:
Enter the value of n: 7

Output:
The sum of odd numbers between 1 and 7 is: 8

In the above example, user given input is 7. So the odd number between 1 to 7 is 1, 3, 5 and 7. So the output is 16.

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 odd 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 odd using the modulo operator (num % 2 != 0).
   • If it is odd, add num to sum.
   • Increment num by 1.
6. Exit the while loop.
7. Print the sum of odd numbers as: “The sum of odd 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 odd 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 or equal to the given number (n).
• Inside the loop, check if the num is an odd number using the modulo (%) operator.
• If the num is odd, add it to the sum variable.
• Increment the num by 1 in each iteration.
• Continue the loop until the counter reaches the given number (n).
• Print the sum of odd numbers.
• Finish the program.

Print the sum of all odd 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 odd numbers between 1 and %d is: %d\n", n, sum);
    return 0;
}

Output

Enter the value of n: 12
The sum of odd numbers between 1 and 12 is: 36

Program Explanation

• The program takes input for the value of n from the user.
• It initializes a variable num to 1, which represents the first odd number to be considered for summation.
• It also initializes a variable sum to 0, which will hold the running sum of odd numbers.
• The program enters a while loop with the condition num <= n to iterate through numbers from 1 to n.
• Inside the while loop, it checks if num is an odd number.
• If num is odd, it adds the value of num to sum.
• It then increments the value of num by 2 since the next odd 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 sum, which represents the sum of all odd numbers between 1 and n.
• The program ends.

Conclusion

The C program successfully calculates and prints the sum of all odd 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 odd numbers, calculates their sum, and displays the result on the screen.

I hope this article will be helpful to understand this program. Please do share.