Return inside loops in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What happens when a return statement is executed inside a loop in Go?

The function immediately stops executing and returns the specified value, exiting the loop and the function at once.

beginner

Can code after a return inside a loop run?

No, once return runs, the function ends immediately, so any code after it inside the loop or function does not run.

intermediate

Why might you use return inside a loop in Go?

To stop the function early when a condition is met, like finding a value or an error, avoiding unnecessary work.

beginner

Example: What does this Go code print?

func findEven(nums []int) int {
  for _, n := range nums {
    if n%2 == 0 {
      return n
    }
  }
  return -1
}

It returns the first even number found in the slice. If none found, it returns -1.

intermediate

Is it good practice to use return inside loops in Go?

Yes, it is common and clear to return early from a function inside a loop when you have the result you want.

What happens when a return is executed inside a loop in Go?

A Only the current loop iteration stops.

B The function exits immediately, stopping the loop.

C The loop continues but the function pauses.

D The loop restarts from the beginning.

In Go, return immediately ends the function, so the loop and function stop.

Can code after a return inside a loop run?

A Yes, always.

B Only if inside another loop.

C No, never.

D Only if inside a conditional.

Once return runs, the function ends immediately, so no further code runs.

Why use return inside a loop?

A To skip the current iteration.

B To restart the loop.

C To pause the function.

D To exit the function early when a condition is met.

Using return inside a loop lets you stop the function early when you find what you need.

What does this code return?

for i := 0; i < 5; i++ {
  if i == 3 {
    return i
  }
}

A 3

B Loop runs forever

C 5

D 0

When i equals 3, the function returns 3 and stops.

Is it okay to use return inside loops in Go?

A Yes, it is common and clear.

B No, it causes errors.

C Only in special cases.

D Only outside functions.

Returning inside loops is a common way to exit functions early in Go.

Explain what happens when a return statement is used inside a loop in Go.

Think about what happens to the function and loop when return runs.

Describe a situation where using return inside a loop is helpful in Go programming.

When might you want to stop searching or processing early?

Practice

1.

What happens when you use return inside a for loop in Go?

easy

A. The function stops immediately and returns the value.

B. Only the current loop iteration stops, and the loop continues.

C. The loop skips the current iteration and moves to the next.

D. The loop runs forever without stopping.

Solution

1. Step 1: Understand the role of return in functions

   In Go, return immediately ends the function and sends back a value.

2. Step 2: Effect of return inside a loop

   When return is inside a loop, it stops the whole function, not just the loop.

3. Final Answer:

   The function stops immediately and returns the value. -> Option A

4. Quick Check:

   Return ends function, not just loop [OK]

Hint: Return inside loop ends function immediately [OK]

Common Mistakes:

• Thinking return only stops the loop
• Confusing return with break
• Assuming loop continues after return

2.

Which of the following Go code snippets correctly uses return inside a for loop to return the first even number from a slice?

func firstEven(nums []int) int {
    for _, n := range nums {
        if n % 2 == 0 {
            // What goes here?
        }
    }
    return -1
}

easy

A. return n

B. break

C. continue

D. return nums

Solution

1. Step 1: Identify what to return inside the loop

   The function should return the first even number found, which is n.

2. Step 2: Use return to stop function and send back the number

   Using return n immediately ends the function and returns the even number.

3. Final Answer:

   return n -> Option A

4. Quick Check:

   Return value inside loop to stop function [OK]

Hint: Use return with value to exit function inside loop [OK]

Common Mistakes:

• Using break instead of return
• Using continue which skips iteration
• Returning the whole slice instead of a number

3.

What is the output of this Go program?

package main
import "fmt"
func findFirstPositive(nums []int) int {
    for _, n := range nums {
        if n > 0 {
            return n
        }
    }
    return 0
}
func main() {
    fmt.Println(findFirstPositive([]int{-3, -2, 0, 5, 10}))
}

medium

A. 10

B. -3

C. 0

D. 5

Solution

1. Step 1: Trace the loop over the slice

   The loop checks each number: -3 (not >0), -2 (not >0), 0 (not >0), 5 (>0).

2. Step 2: Return the first positive number found

   When it reaches 5, it returns 5 immediately, ending the function.

3. Final Answer:

   5 -> Option D

4. Quick Check:

   Return stops at first positive number 5 [OK]

Hint: Return inside loop returns first matching value [OK]

Common Mistakes:

• Assuming loop continues after return
• Returning 0 instead of first positive
• Confusing index with value

4.

Find the error in this Go function that tries to return the first negative number from a slice:

func firstNegative(nums []int) int {
    for _, n := range nums {
        if n < 0 {
            break
        }
    }
    return 0
}

medium

A. Returning 0 instead of -1 when no negative found

B. Missing else statement after if

C. Using break instead of return inside the loop

D. Loop variable should be index, not value

Solution

1. Step 1: Understand break vs return inside loop

   Using break only stops the loop, but the function continues and returns 0.

2. Step 2: Correct usage is return to stop function and return value

   To return the first negative number, use return n inside the if block.

3. Final Answer:

   Using break instead of return inside the loop -> Option C

4. Quick Check:

   Return ends function; break only stops loop [OK]

Hint: Use return, not break, to exit function inside loop [OK]

Common Mistakes:

• Using break instead of return
• Expecting break to return value
• Not returning value inside loop

5.

You want to write a Go function that returns the first string in a slice that starts with the letter 'A'. If none is found, return "Not found". Which code correctly uses return inside the loop?

func findA(words []string) string {
    for _, w := range words {
        if len(w) > 0 && w[0] == 'A' {
            // What goes here?
        }
    }
    return "Not found"
}

hard

A. break

B. return w

C. continue

D. return words[0]

Solution

1. Step 1: Identify the correct return value inside the loop

   The function should return the first word starting with 'A', which is w.

2. Step 2: Use return to immediately end the function and return the word

   Using return w stops the function and returns the found word.

3. Final Answer:

   return w -> Option B

4. Quick Check:

   Return found word inside loop to stop function [OK]

Hint: Return matching item inside loop to stop function early [OK]

Common Mistakes:

• Using break which only stops loop
• Using continue which skips iteration
• Returning wrong element like words[0]