# Find sum of odd numbers from 1 to N in C#

## 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:");

//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}");
}
}
}
```

##### 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:");

while (i <= Number)
{
sum += i;
i += 2;
}

Console.Write(\$"Sum of Odd numbers from 1 to {Number} is : {sum}");
}
}
}
```

##### 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:");

Console.Write("Enter To Number:");

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");
}

}
}
}
```

##### 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:");

Console.Write("Enter To Number:");

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");
}

}

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 aÂ 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.