## C# program to find the sum of all even numbers below a given number:

In this *C#* program, we will learn how to find the *sum* of all *even* numbers in a range from *1 to n*. We will take the value of *n* as input from the user and print the sum of all even numbers.

The easiest way to find the *sum* of all *even numbers* below a given number is by using a *loop*. We can write one loop that will run from *1 to n*, check for each number if it is *even or not* and if it is, add it to a *sum* variable. The *sum* variable is initialized as *0* and it will hold the total sum once the loop ends.

### Method 1: Find the sum of all even numbers below a given number using a for loop:

Let’s try to use a *for loop* to find the sum of all *even numbers* below a given number:

```
using System;
public class Program {
public static void Main(string[] args) {
int i, num, sum = 0;
Console.WriteLine("Enter a number :");
num = Convert.ToInt32(Console.ReadLine());
for(i = 2; i<= num; i++){
if(i % 2 == 0){
sum += i;
}
}
Console.WriteLine("Total sum of all even numbers less than "+num+" is: "+sum);
}
}
```

Here,

- We have initialized three integer variables
*i*,*num*and*sum*.*i*is to use with the*for loop*,*num*to store the user input number and*sum*to hold the sum of the even numbers. - It is reading the number entered by the user and storing it in the variable
*num*. - The
*for loop*runs from*2*to*num*and for each value it finds, it checks for if it is*even*or not. If it is, it is adding that value to*sum*.

It will print output as like below:

```
Enter a number :
20
Total sum of all even numbers less than 20 is: 110
```

### Method 2: Improving the for loop without checking for even:

We can also increment the value of *i* by *2* in the for loop. That will make it easier and we don’t have to check if the current number is divisible by *2* or not.

```
using System;
public class Program {
public static void Main(string[] args) {
int i, num, sum = 0;
Console.WriteLine("Enter a number :");
num = Convert.ToInt32(Console.ReadLine());
for(i = 2; i< num; i +=2){
sum += i;
}
Console.WriteLine("Total sum of all even numbers less than "+num+" is: "+sum);
}
}
```

It will print a similar output:

```
Enter a number :
20
Total sum of all even numbers less than 20 is: 110
```

### Method 3: Using a while loop:

We can also use a *while loop* to do the same thing.

```
using System;
public class Program {
public static void Main(string[] args) {
int i = 2, num, sum = 0;
Console.WriteLine("Enter a number :");
num = Convert.ToInt32(Console.ReadLine());
while(i <= num){
sum += i;
i += 2;
}
Console.WriteLine("Total sum of all even numbers less than "+num+" is: "+sum);
}
}
```

In this program,

- We are using a
*while*loop that runs from*i = 2*to*i = num*. - Inside the
*while loop*, it is incrementing the value of*i*by*2*on each iteration. - It is incrementing the value of
*sum*on each iteration.

It will give similar output.

```
Enter a number :
20
Total sum of all even numbers less than 20 is: 110
```