Return inside loops in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the first even number from the slice.

Go

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

Drag options to blanks, or click blank then click option'

Anum

Bnums

C0

Dnum + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the entire slice instead of the current number.

Returning a fixed number like 0 instead of the actual even number.

The function returns the first even number found in the slice by returning num inside the loop.

2fill in blank

medium

Complete the code to return true if any number in the slice is negative.

Go

func hasNegative(nums []int) bool {
    for _, n := range nums {
        if n < 0 {
            return [1]
        }
    }
    return false
}

Drag options to blanks, or click blank then click option'

A0

Btrue

Cn

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the number itself instead of a boolean.

Returning false inside the loop which stops the check prematurely.

The function returns true immediately when it finds a negative number inside the loop.

3fill in blank

hard

Fix the error in the code to return the index of the first zero in the slice.

Go

func firstZeroIndex(nums []int) int {
    for i, val := range nums {
        if val == 0 {
            return [1]
        }
    }
    return -1
}

Drag options to blanks, or click blank then click option'

Anums[i]

Bval

Ci

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the value instead of the index.

Returning a fixed number like 0 regardless of the position.

The function should return the index i where the first zero is found, not the value.

4fill in blank

hard

Fill both blanks to return the sum of positive numbers only.

Go

func sumPositive(nums []int) int {
    sum := 0
    for _, n := range nums {
        if n [1] 0 {
            sum += [2]
        }
    }
    return sum
}

Drag options to blanks, or click blank then click option'

A>

Bn

C<

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' causing wrong numbers to be summed.

Adding zero instead of the number.

The function checks if a number is greater than zero and adds it to sum.

5fill in blank

hard

Fill all three blanks to create a function that returns the first string longer than 3 characters.

Go

func firstLongString(words []string) string {
    for _, w := range words {
        if len([1]) [2] [3] {
            return w
        }
    }
    return ""
}

Drag options to blanks, or click blank then click option'

Aw

B>

C3

Dwords

Attempts:

3 left

💡 Hint

Common Mistakes

Checking length of the entire slice instead of the current word.

Using '<' instead of '>' causing wrong results.

The function checks the length of each word and returns the first one longer than 3 characters.

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]