Debugging Go Programs

In this lesson, explore debugging go programs through one small Go program, and connect its output to the language rules behind it.

Debugging means locating where observed behavior differs from the expected behavior. Use small reproductions, useful logs, unit tests, and a debugger such as Delve to inspect execution.

A productive sequence is reproduce, identify the wrong value or branch, form a hypothesis and verify a targeted fix.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

Typical debugger workflow: dlv debug, set a breakpoint, inspect variables, and step through code. Delve is a separate development tool; it is not bundled with the Go standard library. See Delve.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import "fmt"

func average(total, count int) float64 {
	if count == 0 {
		return 0
	}
	return float64(total) / float64(count)
}
func main() { fmt.Printf("Average: %.1f\n", average(7, 2)) }

Output

Average: 3.5

Both integers are converted to float64 before division, so the program prints 3.5. Integer division before conversion would lose the fractional part.

• Check intermediate values, not only the final output.
• Avoid leaving sensitive information in debug logs.

Change average to intentionally use integer division and write a test that reveals the bug, then fix it.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Debugging Go Programs in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.