Return inside loops in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Go code with return inside a loop?

Look at this Go function. What will it print when called?

Go

package main
import "fmt"

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

func main() {
    fmt.Println(findFirstEven([]int{1, 3, 5, 6, 8}))
}

A -1

B 6

C 0

D 8

💡 Hint

Remember, return exits the function immediately.

The function returns the first even number it finds. It checks 1, 3, 5 (odd), then 6 (even), so it returns 6 immediately.

❓ Predict Output

intermediate

What does this Go function return?

What value does this function return when called with []int{7, 9, 11}?

Go

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

A 11

B 0

C 7

D -1

💡 Hint

If no even number is found, what does the function return?

Since none of the numbers are even, the loop finishes without returning, so the function returns -1.

🔧 Debug

advanced

Why does this Go function always return 0?

Look at this function. It is supposed to return the first even number from the slice, but it always returns 0. Why?

Go

func findFirstEven(nums []int) int {
    for i := 0; i < len(nums); i++ {
        if nums[i]%2 == 0 {
            break
        }
    }
    return 0
}

A The function returns inside the loop, so it exits too early.

B The loop condition is wrong and never runs.

C The function uses break instead of return, so it never returns the even number found.

D The function returns -1 instead of 0.

💡 Hint

What does break do inside a loop?

break exits the loop but the function continues and returns 0 always. To return the even number, return must be used inside the loop.

📝 Syntax

advanced

Which option causes a compile error in Go?

Which of these code snippets will cause a compile error due to incorrect use of return inside a loop?

A

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

B

1- nruter
}
}    
n nruter        
{ 0 == 2%n fi    
{ smun egnar =: n ,_ rof

C

for _, n := range nums {
    if n%2 == 0 {
        return n
    }
}
return -1

D

for i := 0; i < len(nums); i++ {
    if nums[i]%2 == 0 {
        return nums[i]
    }
}
return -1

💡 Hint

Check if the function always returns a value on all paths.

Option A lacks a return statement after the loop, so if no even number is found, the function has no return value, causing a compile error.

🚀 Application

expert

What is the output of this Go program with nested loops and return?

What will this Go program print?

Go

package main
import "fmt"

func findPair(nums []int, target int) (int, int) {
    for i := 0; i < len(nums); i++ {
        for j := i + 1; j < len(nums); j++ {
            if nums[i]+nums[j] == target {
                return nums[i], nums[j]
            }
        }
    }
    return -1, -1
}

func main() {
    a, b := findPair([]int{1, 3, 5, 7, 9}, 12)
    fmt.Println(a, b)
}

A 3 9

B 5 7

C -1 -1

D 1 11

💡 Hint

The function returns the first pair that sums to the target.

The pairs checked in order are (1,3)=4, (1,5)=6, (1,7)=8, (1,9)=10, (3,5)=8, (3,7)=10, (3,9)=12. The first pair summing to 12 is (3,9), so the function returns 3 and 9 immediately.

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]