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In this blog, we will learn about Iteration i.e Golang For Loop. Iteration is an important part of every programming language and thus Golang has kept it simple.
What we will learn about Golang For Loop:
- Golang For Loop
- Golang For Loop Syntax
- Continue and break keywords in Golang
- Looping through collections
Before Learning about Golang For-Loops, know the basics of Golang:
- Variables in Golang
- Datatypes and Operations in Golang
- Constants in Golang
- Golang Arrays and Slices
- Go Maps and Structs
- Golang If-else and Switch Statements
Golang For Loop
for ; ; { // Statement (s) }
For Loop is the single most loop used in Go Language and thus Go has kept the language simple by just implementing a single kind of loop.
We can use for loops present in Go Language in many different ways so we do not feel the use of other loops like while loop and do-while loop which are present in different languages like (C, C++, Java, Python, etc.)
Example of Golang For Loop:
for i := 1; i <= 5; i++ {
fmt.Println(i)
}Output:
1
2
3
4
5
Golang For Loop Multiple Variables
In C, C++, Java, Python we can use two variables in For-Loop but can we do the same in Go For-Loop.
First see what we used to do in C++ Language For-Loop.
Example (C++):
int i,j;
for(i =0,j = 0; i<=5;i++,j++)
{
std::cout<<i<<" "<<j<<std::endl;
}Output:
0 0 1 1 2 2 3 3 4 4 5 5
But, we cannot do the same in Golang. Golang doesn’t understand comma(,) Operator to separate statements and thus this syntax isn’t possible.
for i := 0, j:=0; i <= 5; i++, j++ {
fmt.Println(i, j)
}Error: – syntax error: unexpected :=, expecting {
Let’s see an approach to do the same in Golang for loop.
for i, j := 0, 0; i <= 5; i, j = i+1, j+1 {
fmt.Println(i, j)
}Output:
0 0
1 1
2 2
3 3
4 4
5 5
Golang For Loop – Outside Initialization
In Go Language, it is not a compulsory thing to initialize variable in for-loop to use it as an iterator. we can make use of pre-initialized variables in go for-loop.
To make use of pre-initialized variables in Golang For-Loop, leave the initialization part and terminate it with using semi-colon (;).
If you don’t use Golang compiler will ask you for initialization.
package main
import (
"fmt"
)
func main() {
i := 0
for i <= 5; i++ {
fmt.Println(i)
}
}Error:
.\main.go:9:18: syntax error: unexpected {, expecting semicolon or newline
.\main.go:10:18: syntax error: i++ used as value
when a semi-colon is provided the compiler will not give you an error.
Example:
i := 0
for ; i <= 5; i++ {
fmt.Println(i)
}Output:
0
1
2
3
4
5
Golang For Loop Scope
When we are using an iterator variable in for-loop its scope is only limited to for-loop.
If the for-loop variable matches the function level scoped variable, the for-loop will not affect the global variable, because for-loop variables have only for-loop scope.
Example:
i := 12
for i := 0; i <= 5; i++ {
fmt.Println(i)
}
fmt.Println("Global i :", i)Output:
0
1
2
3
4
5
Global i : 12
Golang Global variables in For loop
func main() {
i := 12
for ; i <= 15; i++ {
fmt.Println(i)
}
fmt.Println("Global i :", i)
}Output:
12
13
14
15
Global i : 16
In this case, we are using the variable ‘i’ which is the main function scoped and its value will be changed when used in for loop.
Golang Infinite Loop
Actually, Golang doesn’t put us in an infinite loop and it gives an error whenever the compiler thinks the process is taking too long to execute, and thus the infinite loop is not achieved.
Omitting increment operator in Golang for loop can help us to achieve an infinite loop.
Examples of Infinite loop in Golang.
i := 12
for ; i <= 15; {
fmt.Println(i)
}Error: – process took too long
n := 0
for {
fmt.Println(n)
}Output:
0……… Infinite loop
Golang While Loop
Go has only one kind of loop that is For-Loop. This makes The Go Language simple because we only have to work with one kind of loop but also hard because we have to transform the single loop to another loop for our work.
We can convert the Golang For loop to a While loop.
Let’s see.
i := 12
for i <= 15 {
fmt.Println(i)
i++
}Output:
12
13
14
15
One More example of while loop:
Golang program to print the reverse the number.
In this case we have an unknown condition and thus we have to use a while loop i.e Go for loop which is transformed to a while loop.
package main
import (
"fmt"
)
func main() {
reverse := 0
n := 145
for n != 0 {
d := n % 10
reverse = reverse*10 + d
n /= 10
}
fmt.Println("Reverse :", reverse)
}Output:
Reverse : 541
Golang Break
Break keyword is used to break from a loop when a certain condition is met.
The use of the Break keyword is mainly done in an infinite loop to make an exit from the infinite loop.
n := 0
for {
fmt.Println(n)
if( n == 10 ){
break
}
n++
}Output:
0
1
2
3
4
5
6
7
8
9
10
Golang Continue
The Continue keyword is used for skipping certain conditions and not break from the loop. It only skips the loop when a certain condition is met.
Example of Continue Keyword.
Golang Program to print odd numbers.
This program can easily be made without making it complex by using the continue keyword. But this is just an example:
i := 1
for ; i <= 10; i++ {
if i%2 == 0 {
continue
}
fmt.Println(i)
}Output:
1
3
5
7
9
In this example, the continue keyword skips the even number from printing.
Golang Nested Loops
A loop inside a loop is called a nested loop.
Example:
1
12
123
1234
12345
Print the pattern using Golang:
package main
import (
"fmt"
)
func main() {
for i := 1; i <= 5; i++ {
for j := 1; j <= i; j++ {
fmt.Print(j)
}
fmt.Println()
}
}Golang Break Label
When we use the Golang break or continue keyword in the nested loops, it breaks or skips the inner loop i.e child loop and not the outer or parent loop.
for i := 1; i <= 5; i++ {
for j := 1; j <= i; j++ {
if i == 3 {
break
}
fmt.Print(j)
}
fmt.Println()
}Output:
1
12
1234
12345
The 3rd execution breaks and thus just an empty line is printed which is the statement of the outer loop that still executes.
If you want the break or continue to work on the outer loop, make use of labels.
Example:
loop:
for i := 1; i <= 5; i++ {
for j := 1; j <= i; j++ {
if i == 3 {
break loop
}
fmt.Print(j)
}
fmt.Println()
}Output:
1
12
Golang Range
Go for loop can also be used to loop in a collection like Arrays, Maps, Slices, etc to get key, value.
Golang range keyword is used for looping through a collection.
Golang For loop Slice
Example:
s := []string{"Divyanshu Shekhar", "Hritul Priya"}
for k, v := range s {
fmt.Println(k, v)
}Output:
0 Divyanshu Shekhar
1 Hritul Priya
The Key Prints the indexes and the values are the real values present at the indexes.
Golang For Loop Map
m := map[string]int{
"DS": 17,
"HP": 13,
}
for k, v := range m {
fmt.Println(k, v)
}Output:
DS 17
HP 13
In this example, a map is used and thus the key changes to the key and value of the map.
when you don’t need the key and just want to work with values, you can do something like this:
for _, v := range m {
fmt.Println(v)
}This states that the key is not stored in memory as we don’t need it.
Read Why Golang is called the future of server-side language?
Read Official Docs to know more about Golang For Loops.
