Go Variables

In Go, variables act as containers for storing various types of data. By using variables, you can store values such as numbers, text, or logical states and use them throughout your program.

Go Variable Types

Go supports several variable types, such as:

• int: For storing whole numbers, like 42 or -100.
• float32: For storing numbers with decimal points, such as 3.14 or -9.81.
• string: For storing textual data, like "Hello Go!" (enclosed in double quotes).
• bool: For storing logical states, which can be either true or false.

The specific data type determines how the variable behaves and what kind of data it can store. For more details, refer to the Go Data Types lesson.

Declaring Variables

In Go, variables can be declared in two main ways:

Declaring with the var Keyword

The var keyword lets you explicitly define a variable’s name, type, and optionally its value.

Syntax:

var variableName type = value

You must specify either the type or the value (or both) when using var.

Declaring with the := Syntax

Go also supports shorthand variable declarations using :=. Here, the compiler determines the variable’s type based on its assigned value.

Syntax:

variableName := value

This shorthand requires assigning a value during declaration.

Variable Declaration with Initial Values

When the value of a variable is known at the time of declaration, it can be initialized in a single step.

Example:

package main

import ("fmt")

func main() {
  var brand1 string = "Yamaha"  // Explicitly specifying the type
  var brand2 = "Honda"          // Type is inferred
  speed := 150                  // Type is inferred as int

  fmt.Println(brand1)
  fmt.Println(brand2)
  fmt.Println(speed)
}

Here:

• brand1 is explicitly defined as a string.
• brand2 and speed have their types inferred as string and int, respectively.

Variable Declaration without Initial Values

In Go, if you declare a variable without initializing it, the compiler assigns it a default value based on its type.

Example:

package main

import ("fmt")

func main() {
  var model string
  var year int
  var active bool

  fmt.Println(model)  // Default value: ""
  fmt.Println(year)   // Default value: 0
  fmt.Println(active) // Default value: false
}

In this example:

• model defaults to an empty string "".
• year defaults to 0.
• active defaults to false.

Assigning Values After Declaration

You can assign a value to a variable after it has been declared.

Example:

package main

import ("fmt")

func main() {
  var brand string
  brand = "Suzuki"
  fmt.Println(brand)
}

Note: Variables declared using := must have a value during their declaration.

Differences Between var and :=

There are subtle differences between var and :=:

Example with var Outside Functions:

package main

import ("fmt")

var brand string = "Honda" // Declaring variable outside a function

func main() {
  fmt.Println(brand)
}

Example with := Outside Functions:

package main

import ("fmt")

brand := "Yamaha" // This will throw an error

func main() {
  fmt.Println(brand)
}

Result:
The code produces an error because := cannot be used outside a function:

./prog.go:5:1: syntax error: non-declaration statement outside function body