Calculate Sum of N Natural Numbers in C using Recursion

Sum of N Natural Numbers in C using Recursion Program Description:

Write a Program to Calculate the Sum of N Natural Numbers in C using Recursion. The program accepts a number from the user and calculates the sum of the first n natural numbers. We need to use the recursion and should not use the C Loops ( like for, while, and do-while) to calculate the sum.

Example Input and Output:

Input:

Enter a Number: 10

Output:

Sum of first 10 numbers is : 55

What is Recursion:

Function calling itself is called recursion. Any function which calls itself is called a recursive function.

Here is the pseudo-code of recursion.

Pre-Requisites:

• C Functions
• Recursion in C

Sum of N Natural Numbers in C using Recursion Algorithm / Explanation:

1. Take the input from the user and store it in the variable named n.
2. Check if the n is a negative number, If so display an error message ( ERROR! Enter a Valid Number). Ask for the user input again. Take the program control back to the start of the program using the Goto Statement in C
   • Use goto INPUT; and INPUT: labels to jump to the start of the program.
3. Once we got the positive number, Proceed to the next step.
4. Create a function called sumOfNumbers. The sumOfNumbers function takes an integer as input and calculates the sum of the first n natural numbers.
   • The sumOfNumbers uses recursion to calculate the sum of n numbers and returns it.
   • The base condition for the recursion is n == 0. So our recursive calls will stop once the formal argument n reaches the value .
   • If the formal argument n value is not equal to zero. Then make a recursive call to the sumOfNumbers function with n-1 as an argument. Also, add the value of the formal argument to the return value of the function call ( n + sumOfNumbers(n-1))
   • The above recursive calls continue until we reach the base condition.
5. Call the sumOfNumbers function from the main function, Which returns the sum of first n natural numbers. Store the return value in result variable and display the result onto the console using the printf

Sum of N Natural Numbers in C using Recursion Program:

Here is the code for the above algorithm

Here are the prototype details of the sumOfNumbers function

• int sumOfNumbers(int);
• function_name: sumOfNumbers
• argument_list: int
• return_value : int

Program output:

Compile and run the program.

Test Case 1: Positive Numbers:

Test Case 2: Negative Numbers:

As you can see from the above output, We are getting the desired results.

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