Variables and control flow

In plain English

A variable holds a value, and Go lets you declare one with var for an explicit statement or with := for a short inferred declaration inside a function. A zero value is the automatic default a variable gets before you assign to it, like 0 for numbers, false for booleans and "" for strings. if/else runs one block or the other based on a condition, and switch chooses between several named cases without needing a break. Go has one loop, for, which covers counting, ranging over values and looping while a condition holds.

Step by step

1. 1Declare a variable with var or := depending on how much you want to spell out.
2. 2Read the zero value your variable starts with before assigning.
3. 3Branch with if/else when there are two outcomes.
4. 4Choose between many named cases with switch.
5. 5Loop with for for counting, ranging and conditions.

package main

import "fmt"

var maxLessons = 14

func main() {
    var minutes int
    var published bool
    fmt.Println(minutes, published)

    minutes = 12
    published = true
    title := "Variables and control flow"

    if published && minutes >= maxLessons {
        fmt.Println(title, "is long")
    } else {
        fmt.Println(title, "is short")
    }

    switch minutes {
    case 5:
        fmt.Println("quick")
    case 12:
        fmt.Println("steady")
    default:
        fmt.Println("other")
    }

    for i := 1; i <= 3; i++ {
        fmt.Println("lesson", i)
    }
}

Common mistakes

• Declaring a variable with := at package scope fails, because := is only allowed inside functions.
• Forgetting that a fresh variable starts at its zero value can hide bugs when you assume it is already set.
• Writing a while loop with while does not work in Go, because for is the only loop keyword.
• Assuming switch needs a break after each case is wrong; Go cases do not fall through by default.