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**How to Find the sum of odd numbers from 1 to N in C# with Examples**

In this article, I am going to discuss **How to find the sum of odd numbers from 1 to N in C#** with Examples. Please read our previous article, where we discussed **How to find the sum of even numbers from 1 to N in C#**. Here, in this article, first, we will discuss what are Odd Numbers, then we will discuss how to find the sum of odd numbers between a range of numbers and finally, we will see how to implement the sum of odd number Program in C#.

**What are Odd Numbers?**

An odd number is a number that is not divisible by 2. The remainder in the case of an odd number is always 1. Example: 1, 3, 5, 7, 9, etc.

**How to check if a number is odd or not?**

If a number is not divisible by 2 then it is an odd number.

if(number % 2 == 1)

Â Â Â Â Â This is an odd number.

else

Â Â Â Â Â This is not an odd number.

**How to Print the sum of odd numbers from 1 to N in C#?**

In the case of numbers from 1 to 100, there are 50 odd numbers and 50 even numbers. This basically means every second number is an odd number.

Example: 1, 3, 5, 7, 9, etc. are odd numbers

1 is an odd number

then 3 (2 is an even number)

then 5 (4 is an even number)

5 then 7 (6 is an even number) and so on.

**Algorithm to find the sum of odd numbers**

**Step1**: Take a variable named N and store the value of the upper limit of N.

**Step2**: Take one more variable named sum to store the result of the calculation.

**Step3**: Take a for loop with variable i which be initialized with 1 and in condition expression check for (i<=N) and

**Step4**: In the third expression of for loop increment the value of i with 2(because every second number is odd/even).

**Â Â Â Â Â Â for(int i=1;i<=N;i=i+2)**

**Â Â Â Â Â Â Â Â Â Â sum += i; //sum = sum + i;**

**Example: C# Program to find the sum of odd numbers from 1 to n**

The following C# Program will find the sum of odd numbers from 1 to N using for loop.

using System; namespace DotNetTutorials { class SumOfEvenNumbers { static void Main(string[] args) { int sum = 0; Console.Write("Enter value a Number:"); int Number = Convert.ToInt32(Console.ReadLine()); //start with 1 //1+2 = 3 //3+2 = 5 for (int i = 1; i <= Number; i += 2) { sum += i; } Console.Write($"Sum of Odd numbers from 1 to {Number} is : {sum}"); Console.ReadLine(); } } }

**Output:**

**Example: Using while loop**

The following C# Program will find the sum of odd numbers from 1 to N using the while loop.

using System; namespace DotNetTutorials { class SumOfEvenNumbers { static void Main(string[] args) { int sum = 0, i = 1; Console.Write("Enter value a Number:"); int Number = Convert.ToInt32(Console.ReadLine()); while (i <= Number) { sum += i; i += 2; } Console.Write($"Sum of Odd numbers from 1 to {Number} is : {sum}"); Console.ReadLine(); } } }

**Output:**

**Finding the sum of odd numbers between a Range of Numbers:**

The examples we have discussed earlier are used to find the sum of odd numbers starting from 1. But what if we donâ€™t want to start from 1, instead we can give any numbers, letâ€™s say we want to find the sum of odd numbers from 50 to 100. The following C# program will ask the user to enter two numbers (the first number should be less than the second number) and then calculate the sum of odd numbers.

using System; namespace DotNetTutorials { class SumOfEvenNumbers { static void Main(string[] args) { int sum = 0; Console.Write("Enter From Number:"); int FromNumber = Convert.ToInt32(Console.ReadLine()); Console.Write("Enter To Number:"); int ToNumber = Convert.ToInt32(Console.ReadLine()); if (FromNumber < ToNumber) { for (int i = FromNumber; i <= ToNumber; i++) { if (i % 2 == 1) sum += i; } Console.Write($"Sum of Odd numbers from {FromNumber} to {ToNumber} is : {sum}"); } else { Console.Write("Invalid From and To Numbers"); } Console.ReadLine(); } } }

**Output:**

**Using Function**

In the below C# program, we have created one method to find the sum of odd numbers between a range of numbers.

using System; namespace DotNetTutorials { class SumOfEvenNumbers { static void Main(string[] args) { int sum = 0; Console.Write("Enter From Number:"); int FromNumber = Convert.ToInt32(Console.ReadLine()); Console.Write("Enter To Number:"); int ToNumber = Convert.ToInt32(Console.ReadLine()); if (FromNumber < ToNumber) { sum = FindSumOfOddNumbers(sum, FromNumber, ToNumber); Console.Write($"Sum of Odd numbers from {FromNumber} to {ToNumber} is : {sum}"); } else { Console.Write("Invalid From and To Numbers"); } Console.ReadLine(); } private static int FindSumOfOddNumbers(int sum, int FromNumber, int ToNumber) { for (int i = FromNumber; i <= ToNumber; i++) { if (i % 2 == 1) sum += i; } return sum; } } }

**Output:**

In the next article, I am going to discuss **How to Convert** **a**Â **Kilogram to Gram and vice versa in C#** with Examples. Here, in this article, I try to explain **How to Find the sum of odd numbers from 1 to N in C#** with Examples and I hope you enjoy this How to Find the sum of odd numbers from 1 to N article.

**About the Author: Pranaya Rout**

Pranaya Rout has published more than 3,000 articles in his 11-year career. Pranaya Rout has very good experience with Microsoft Technologies, Including C#, VB, ASP.NET MVC, ASP.NET Web API, EF, EF Core, ADO.NET, LINQ, SQL Server, MYSQL, Oracle, ASP.NET Core, Cloud Computing, Microservices, Design Patterns and still learning new technologies.