This post we will cover three programs to find the sum of natural numbers

- Sum of first n natural numbers entered by the user
- Sum of first n natural numbers using for loop
- Sum of first n natural numbers Recursive function

Natural numbers are positive integers or whole numbers which starts from 0,1, 2 …. n. These also called nonpositive numbers. This post is about calculating the sum of natural numbers from 1 to n where n is read from console by the user.

To understand this programs, You should have an understanding of following golang features.

### Example program 1- Sum of first n natural numbers Entered by user

The below program takes an input number from command line console from a user and calculates the sum of natural numbers up to a given number

```
package main
import (
"fmt"
)
func main() {
//reading an multiple input string
var number int
fmt.Print("Please enter number:")
fmt.Scanln(&number)
sumResult := 0
for i := 0; i <= number; i++ {
sumResult += i
}
fmt.Printf("Sum of %d numbers is %d", number, sumResult)
}
```

Output is

```
Please enter number:10
Sum of 10 numbers is 55
```

The above program read an input from the user using the Scanln function, store the number in a variable number.

Using for loop, iterate and calculates the values from 0 up to n

Finally, a sum is printed to console

### Example program 2- Sum of natural numbers using for loop

In this program, Instead of taking input from the user, the variable value is fixed, Like an above program, for loop is used to calculate up to a given number.

Finally printed value to the console

```
package main
import (
"fmt"
)
func main() {
max := 10
sumResult := 0
for i := 0; i <= max; i++ {
sumResult += i
}
fmt.Printf("Sum of %d numbers is %d", max, sumResult)
}
```

Output is

```
Sum of 10 numbers is 55
```

### Example program 3- Recursion function Sum of natural numbers

```
package main
import (
"fmt"
)
func sumNatural(numb int) int {
if numb != 0 {
return numb + sumNatural(numb-1)
} else {
return numb
}
}
func main() {
number := 10
fmt.Printf("Sum of %d numbers is %d", number, sumNatural(number))
}
```

Output is

```
Sum of 10 numbers is 55
```

In the above program, sumNatural recursive function is declared. This will be called in the main function initially at first using sumNatural(10) function.

the number 10 is added the result of sumNatural(9). next function call will be fired from sumNatural which again calls sumNatural(8) and add this result. This sequence of the process will continue until numb is equal to 0.

recursive call execution will be stopped When numb is zero and finally returned the result to the main function