Undefined Variable

Why This Happens

Go requires variables to be declared before use. This error appears when you reference a variable that does not exist in the current scope, misspell a variable name, or try to use a variable declared in a different scope like inside an if block.

The Problem

func main() {
    if true {
        x := 42
    }
    fmt.Println(x) // undefined: x
}

The Fix

func main() {
    var x int
    if true {
        x = 42
    }
    fmt.Println(x)
}

Step-by-Step Fix

1. 1

   Identify the undefined name

   Read the error to find the exact name that is undefined.

2. 2

   Check the scope

   Verify the variable is declared in a scope that is accessible from the line that uses it.

3. 3

   Fix the scope or typo

   Either declare the variable in the outer scope, fix the typo, or import the missing package.