## C# program to find the sum of all numbers from 1 to n:

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

This program can be solved by using a *loop*. In this post, we will learn how to find the *sum* by using a *for loop* and by using a *while loop*. Each loop will run from *1* to *n* and print out the *sum* at the end.

### By using a for loop:

Let’s first use a *for loop* to solve this. Below is the complete algorithm this program will use:

- Initialize one variable as
*0*to store the total sum. - Read the value
*n*as user-input from the user. - Run one
*for loop*from*1*to*n*. - Inside the loop, adds the current value of the
*for loop*to the*sum variable*. At the end of the program, print the value of*sum*.

C# program that uses the above algorithm:

```
using System;
public class Program {
public static void Main(string[] args) {
int i, n, sum = 0;
Console.WriteLine("Enter the value of n :");
n = Convert.ToInt32(Console.ReadLine());
for(i = 1; i<= n; i++){
sum += i;
}
Console.WriteLine("Total sum: "+sum);
}
}
```

Here,

*sum*is the variable to hold the total sum. It is initialized as*0*.- The value of
*n*is taken as user-input. - The
*for loop*runs from*i = 1*to*i = n*. Inside the loop, it is adding the value of*i*to*sum*. - Finally, it is printing the value of
*sum*.

It will print the below output:

```
Enter the limit :
5
Total sum: 15
```

### By using a while loop:

We can also use a *while loop* to find the *sum*. Below is the complete program:

```
using System;
public class Program {
public static void Main(string[] args) {
int i = 1, n, sum = 0;
Console.WriteLine("Enter the value of n :");
n = Convert.ToInt32(Console.ReadLine());
while(i <= n){
sum += i;
i++;
}
Console.WriteLine("Total sum: "+sum);
}
}
```

Here, we initialized the value of *i* as *1*. The *while loop* runs and adds the value of *i* to *sum*. Inside the *while loop*, we are incrementing the value of *i* by *1* after each iteration.

After the loop ends, we are printing the total sum i.e. *sum* to the user.

This will print similar output.

### Using a formula:

We can also solve this by using the below formula:

`Sum from 1 to n = n * (n + 1)/2;`

So, if we can read the value of *n*, we can find out the sum by using this simple formula. This is a quick way to find the sum from *1 to n*. Because, we don’t have to run a *loop* for that.

If you are trying to find the sum for a big value, it will take time if we run a loop, but it will be quicker if we use the above formula.

Below is the *C# program*:

```
using System;
public class Program {
public static void Main(string[] args) {
int i = 1, n, sum = 0;
Console.WriteLine("Enter the value of n :");
n = Convert.ToInt32(Console.ReadLine());
sum = n * (n + 1)/2;
Console.WriteLine("Total sum: "+sum);
}
}
```

It will print similar output.