Common errors

Go reports most mistakes when it builds, before anything runs. A runtime failure is a panic: it prints panic: with the reason, then the stack of calls with file and line, and the program exits with status 2.

• declared and not used: x — remove the variable or use it; assign to _ to discard a value on purpose.
• "os" imported and not used — remove the import.
• undefined: x — a typo, a variable declared in another block, or a function in a file that is not part of the build (a main* or test_* file).
• cannot use x (variable of type int) as string value — convert explicitly: strconv.Itoa(x), float64(x).
• missing return — every path through a function with a result type must return.
• panic: runtime error: index out of range [3] with length 3 — indexes go from 0 to len(s)-1.
• panic: assignment to entry in nil map — create the map with make or map[K]V{} first.
• panic: runtime error: invalid memory address or nil pointer dereference — a pointer, map or interface is nil where a value was expected.
• fatal error: all goroutines are asleep - deadlock! — every goroutine is waiting on a channel or lock that nothing will release.

package main

import (
	"fmt"
	"strconv"
)

func main() {
	total := 0
	for _, v := range []string{"10", "x", "7"} {
		n, err := strconv.Atoi(v)
		if err != nil {
			fmt.Printf("skipped %q\n", v)
			continue
		}
		total += n
	}
	fmt.Println("total:", total)
}

skipped "x"
total: 17