# Golang program to calculate the sum of all even numbers

In this tutorial, we will be discussing the program to find the sum of all even numbers in Golang programming.

But before writing the code for this, let’s briefly discuss even numbers.

### Even Numbers

An even number is a number that is completely divisible by 2 and its remainder is always 0. A simple way to check whether a number is an even number or not is to check its last digit. If the last digit is 0, 2, 4, 6, or 8, then the number is said to be an even number.

## Iterate through the first n even numbers and add them

### Example

• Number = 4

Sum of first 4 even numbers = 20

First 4 even numbers are- 2, 4, 6, and 8

Sum of these numbers = 2 + 4 + 6 + 8

= 20

### Algorithm

Step 1 − Declare a variable ‘num’ for storing the number.

Step 2 − Declare a variable ‘nextEven’ for storing the number 2.

Step 3 − Declare a variable ‘sum’ for storing the sum of even numbers and initialize it with 0.

Step 4 − Create a for loop starting from 1 and run it till it is less than or equal to ‘num’.

Step 5 − Calculate the sum by adding the next even number back to the sum until the for loop ends.

Step 6 − All even numbers have a difference of 2. Calculate the next even number by adding 2 to the current number.

Step 7 − Once the for loop ends, print the result stored in ‘sum’.

### Example

package main

// fmt package allows us to print formatted strings
import "fmt"
func main() {
fmt.Println("Program to calculate the sum of all even numbers \n")

// declaring variable ‘num’ for storing the number
var num int = 4

// declaring variable ‘nextEven’ for storing the next even number
var nextEven int = 2

// declaring variable ‘sum’ for storing the sum of all even numbers
var sum int = 0
for x := 1; x <= num; x++ {

// calculating sum of even numbers
sum = sum + nextEven

// calculating next even number
nextEven = nextEven + 2
}

// printing the results
fmt.Println("Finding the sum of first", num, "Even numbers")
fmt.Println("Therefore, Sum of even numbers : ", sum)
}


### Output

Program to calculate the sum of all even numbers

Finding the sum of first 4 Even numbers
Therefore, Sum of even numbers :  20


### Description of code

• var num int = 4 − In this line, we are declaring the variable num for storing the number for which the user wants to calculate the sum of all even numbers.

• var nextEven int = 2 − We will store the value of the next even number in this variable. Initially, we assigned the value 2 to it.

• var sum int = 0 − We will be storing the resultant sum of the even numbers in this variable and will initialize it with 0 in the beginning.

• for x := 1; x <= num; x++ − This for loop will be used to count the sum of the even numbers. It will start from 1 and will run until the value of ‘x’ is less than or equal to ‘num’.

• sum = sum + nextEven − In this, we are calculating the sum by adding the next even number back to sum until the for loop ends.

• nextEven = nextEven + 2 − This is used to calculate the next even number. All even numbers have a difference of 2, that is why we are adding 2 in order to generate the next even number.

• fmt.Println("Therefore, Sum of even numbers : ", sum) − printing the calculated sum of all even numbers until ‘num’.

## Using the formula for calculating the sum of all even numbers

### Formula

$$\mathrm{Sum\: of\: \: first\: 'n'\: even\: numbers = n \ast (n + 1)}$$

### Example

• Number = 10

Sum of first 10 even numbers = num * (num + 1)

10 * (10 + 1)

= 110

### Algorithm

Step 1 − Declare a variable for storing the number- ‘num’.

Step 2 − Declare a variable for storing the sum of all even numbers- ‘sum’ and initialize it with 0.

Step 3 − Calculate the sum using the formula num * (num + 1) and store it in the ‘sum’ variable in the function calculateSumOfEvenNumbers().

Step 4 − Print the calculated sum, i.e, the value stored in the variable ‘sum’ by calling the calculateSumOfEvenNumbers() function from within the main() function.

### Example

package main

// fmt package allows us to print formatted strings
import "fmt"
func calculateSumOfEvenNumbers(num int) int {

// declaring variable ‘sum’ for storing the sum of all even numbers
var sum int = 0

// calculating sum
sum = num * (num + 1)
return sum
}
func main() {

// declaring variable ‘num’ for storing the number
var num int = 10
var sum int
fmt.Println("Program to calculate the sum of all even numbers \n")

// calling function calculateSumOfEvenNumbers() for
// calculating the sum of even numbers
sum = calculateSumOfEvenNumbers(num)

// printing the results
fmt.Println("Finding the sum of first", num, "Even numbers")
fmt.Println("Therefore, Sum of even numbers : ", sum)
}


### Output

Program to calculate the sum of all even numbers

Finding the sum of first 10 Even numbers
Therefore, Sum of even numbers :  110


### Description of code

• var num int = 10, var sum int − In this line, we are declaring the variables ‘num’ and ‘sum’.

• calculateSumOfEvenNumbers(num int) int − This is the function where we are calculating the sum of even numbers. The function has the variable ‘num’ of data type int as the parameter and also has a return type value of data type int.

• sum = num * (num + 1) − We are finding the sum of all even numbers using this formula- num * (num + 1).

• return sum − for returning the calculated sum of all even numbers

• sum = calculateSumOfEvenNumbers(num) − We are calling the function calculateSumOfEvenNumbers() and storing the calculated value in the ‘sum’ variable.

• fmt.Println("Therefore, Sum of even numbers : ", sum) − printing the calculated sum of all even numbers.

## Conclusion

This is all about calculating the sum of even numbers using two approaches. The second approach is better in terms of time complexity and modularity. You can explore more about Golang programming using these tutorials.