Go Program to Find Sum of N Natural Numbers

In Go, you can find the sum of n natural numbers by using a loop or the formula sum = n * (n + 1) / 2. For example, sum := n * (n + 1) / 2 calculates the sum directly.

Examples

Input5

OutputSum of first 5 natural numbers is 15

Input10

OutputSum of first 10 natural numbers is 55

Input1

OutputSum of first 1 natural numbers is 1

How to Think About It

To find the sum of the first n natural numbers, think of adding all numbers from 1 up to n. You can do this by adding each number one by one using a loop, or use the simple math formula n * (n + 1) / 2 which gives the same result instantly.

Algorithm

1

Get the input number n from the user

2

Calculate the sum using the formula sum = n * (n + 1) / 2

3

Print the sum

Code

go

package main

import "fmt"

func main() {
    var n int
    fmt.Print("Enter a positive integer: ")
    fmt.Scan(&n)
    sum := n * (n + 1) / 2
    fmt.Printf("Sum of first %d natural numbers is %d\n", n, sum)
}

Output

Enter a positive integer: 5
Sum of first 5 natural numbers is 15

Dry Run

Let's trace the input 5 through the code

1

Input

User enters n = 5

2

Calculate sum

sum = 5 * (5 + 1) / 2 = 5 * 6 / 2 = 30 / 2 = 15

3

Output

Print 'Sum of first 5 natural numbers is 15'

n	sum
5	15

Why This Works

Step 1: Input reading

The program reads the number n from the user using fmt.Scan.

Step 2: Sum calculation

It uses the formula n * (n + 1) / 2 which adds all numbers from 1 to n efficiently.

Step 3: Output display

The program prints the result using fmt.Printf with formatted output.

Alternative Approaches

Using a loop

go

package main

import "fmt"

func main() {
    var n, sum int
    fmt.Print("Enter a positive integer: ")
    fmt.Scan(&n)
    for i := 1; i <= n; i++ {
        sum += i
    }
    fmt.Printf("Sum of first %d natural numbers is %d\n", n, sum)
}

This method uses a loop to add numbers one by one, which is easy to understand but slower for very large n.

Using recursion

go

package main

import "fmt"

func sumNatural(n int) int {
    if n == 1 {
        return 1
    }
    return n + sumNatural(n-1)
}

func main() {
    var n int
    fmt.Print("Enter a positive integer: ")
    fmt.Scan(&n)
    fmt.Printf("Sum of first %d natural numbers is %d\n", n, sumNatural(n))
}

This method uses recursion to add numbers, which is elegant but can cause stack overflow for very large n.

Complexity: O(1) time, O(1) space

Time Complexity

Using the formula, the sum is calculated in constant time without loops.

Space Complexity

Only a few variables are used, so space is constant.

Which Approach is Fastest?

The formula method is fastest; loop and recursion methods take O(n) time.

Approach	Time	Space	Best For
Formula	O(1)	O(1)	Fastest calculation for any n
Loop	O(n)	O(1)	Simple and easy to understand
Recursion	O(n)	O(n)	Elegant but uses more memory