Go Constants #

When you need a value that should never change throughout the execution of a program, you can use a constant.

Constants are unchangeable and read-only values declared using the const keyword.

✅ Syntax of Declaring a Constant #

const CONSTNAME type = value

👉 Important: The value of a constant must be assigned when declared.

✅ Example: Declaring a Constant #

package main

import "fmt"

const PI = 3.14

func main() {
    fmt.Println(PI)  // Output: 3.14
}

✅ Constant Rules #

• Constant names follow the same naming rules as variables.
• By convention, constant names are often written in uppercase letters to easily distinguish them.
• Constants can be declared inside and outside functions.

✅ Types of Constants #

1️⃣ Typed Constants #

Declared with an explicit type.

Example: #

package main

import "fmt"

const A int = 1

func main() {
    fmt.Println(A)  // Output: 1
}

2️⃣ Untyped Constants #

Declared without specifying a type. The type is inferred from the value.

Example: #

package main

import "fmt"

const A = 1

func main() {
    fmt.Println(A)  // Output: 1
}

✅ Constants Are Read-Only #

Once declared, a constant’s value cannot be changed.

Example: #

package main

import "fmt"

func main() {
    const A = 1
    A = 2  // ❌ Error: cannot assign to A
    fmt.Println(A)
}

⚠️ Result:

./prog.go:8:7: cannot assign to A

✅ Multiple Constants Declaration #

For better organization, you can declare multiple constants in a block.

Example: #

package main

import "fmt"

const (
    A int    = 1
    B        = 3.14
    C        = "Hi!"
)

func main() {
    fmt.Println(A)  // Output: 1
    fmt.Println(B)  // Output: 3.14
    fmt.Println(C)  // Output: Hi!
}

🚀 Using constants improves your program’s readability and prevents accidental changes to important values.