Return inside loops in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the first even number found in the array.

Java

public int findFirstEven(int[] numbers) {
    for (int num : numbers) {
        if (num % 2 == 0) {
            return [1];
        }
    }
    return -1;
}

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

Anum + 1

Bnumbers

C0

Dnum

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the whole array instead of the number.

Returning a fixed number like 0 instead of the found number.

The method returns the first even number found in the array, which is the variable num inside the loop.

2fill in blank

medium

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

Java

public boolean hasNegative(int[] numbers) {
    for (int num : numbers) {
        if (num < 0) {
            return [1];
        }
    }
    return false;
}

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

Anum

Btrue

Cfalse

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Returning false inside the loop.

Returning the number instead of a boolean.

The method returns true immediately when it finds a negative number.

3fill in blank

hard

Fix the error in the code to return the index of the first zero in the array, or -1 if none found.

Java

public int findFirstZero(int[] arr) {
    for (int i = 0; i < arr.length; i++) {
        if (arr[i] == 0) {
            return [1];
        }
    }
    return -1;
}

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

Ai

Barr[i]

C0

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the value arr[i] instead of the index.

Returning a fixed number like 0.

The method should return the index i where the zero is found, not the value at that index.

4fill in blank

hard

Fill both blanks to return the sum of positive numbers in the array.

Java

public int sumPositive(int[] nums) {
    int sum = 0;
    for (int [1] = 0; [2] < nums.length; i++) {
        if (nums[i] > 0) {
            sum += nums[i];
        }
    }
    return sum;
}

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

Ai

Bnum

Cj

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in initialization and condition.

Using a variable that is not an integer index.

The loop variable i is used for initialization and condition to iterate over the array.

5fill in blank

hard

Fill all three blanks to return true if all numbers in the array are positive.

Java

public boolean allPositive(int[] arr) {
    for (int [1] = 0; [2] < arr.length; [3]++) {
        if (arr[i] <= 0) {
            return false;
        }
    }
    return true;
}

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

Ai

Bj

Dk

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in the for loop parts.

Using a variable not declared in the loop.

The loop variable i is used consistently for initialization, condition, and increment.

Practice

1. What happens when a return statement is executed inside a loop in a Java method?

easy

A. The method stops immediately and returns the specified value.

B. The loop skips the current iteration and continues.

C. The loop finishes all iterations before returning.

D. The method throws an error and stops.

Solution

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

   The return statement immediately ends the method and sends back a value to the caller.

2. Step 2: Effect of return inside a loop

   When return is inside a loop, the method stops as soon as return runs, so the loop does not continue.

3. Final Answer:

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

4. Quick Check:

   return inside loop stops method [OK]

Hint: Return inside loop ends method immediately [OK]

Common Mistakes:

• Thinking loop continues after return
• Confusing return with continue or break
• Assuming method runs all loop iterations

2. Which of the following is the correct syntax to return an integer value from inside a for loop in Java?

easy

A. for(int i=0; i<5; i++) { return; }

B. for(int i=0; i<5; i++) { if(i==3) return i; }

C. for(int i=0; i<5; i++) { return i +; }

D. for(int i=0; i<5; i++) { return i i; }

Solution

1. Step 1: Check syntax of return statement

   Return must specify a value matching method return type; here, returning i (an int) is correct.

2. Step 2: Identify syntax errors in options

   for(int i=0; i<5; i++) { return; } returns nothing in an int method (error). Options C and D have invalid expressions after return.

3. Final Answer:

   for(int i=0; i<5; i++) { if(i==3) return i; } -> Option B

4. Quick Check:

   Correct return syntax inside loop [OK]

Hint: Return must match method type and be valid expression [OK]

Common Mistakes:

• Omitting return value in non-void method
• Using invalid expressions after return
• Syntax errors like missing semicolons or operators

3. What is the output of this Java method?

public static int findFirstEven(int[] nums) {
    for (int n : nums) {
        if (n % 2 == 0) {
            return n;
        }
    }
    return -1;
}

public static void main(String[] args) {
    System.out.println(findFirstEven(new int[]{3, 7, 8, 10}));
}

medium

A. 3

B. 7

C. 8

D. -1

Solution

1. Step 1: Trace the loop over array elements

   The loop checks each number: 3 (odd), 7 (odd), then 8 (even).

2. Step 2: Return on first even number

   When 8 is found even, method returns 8 immediately, stopping the loop.

3. Final Answer:

   8 -> Option C

4. Quick Check:

   First even number returned = 8 [OK]

Hint: Return stops loop at first matching condition [OK]

Common Mistakes:

• Assuming method returns last even number
• Ignoring return stops loop early
• Confusing output with array contents

4. Identify the error in this Java method:

public static int findPositive(int[] arr) {
    for (int x : arr) {
        if (x > 0) {
            return x;
        } else {
            return 0;
        }
    }
    return -1;
}

medium

A. The method should return a boolean, not int.

B. The method has a syntax error in the for loop.

C. The method never returns a value.

D. The method returns 0 too early, not checking all elements.

Solution

1. Step 1: Analyze the return statements inside the loop

   Inside the loop, both if and else branches have return, so method returns on first element always.

2. Step 2: Understand the logic flaw

   If first element is not positive, method returns 0 immediately without checking others.

3. Final Answer:

   The method returns 0 too early, not checking all elements. -> Option D

4. Quick Check:

   Return inside else stops loop too soon [OK]

Hint: Return in both if and else inside loop stops early [OK]

Common Mistakes:

• Expecting loop to check all elements
• Ignoring that return ends method immediately
• Confusing return with continue or break

5. You want to write a method that returns the first negative number from an array, or 0 if none found. Which code correctly uses return inside a loop to do this efficiently?

hard

A. public static int firstNegative(int[] arr) { for(int n : arr) { if(n < 0) return n; } return 0; }

B. public static int firstNegative(int[] arr) { for(int n : arr) { if(n < 0) return n; else return 0; } }

C. public static int firstNegative(int[] arr) { int result = 0; for(int n : arr) { if(n < 0) result = n; } return result; }

D. public static int firstNegative(int[] arr) { for(int n : arr) { if(n < 0) break; } return 0; }

Solution

1. Step 1: Check return usage inside loop

   public static int firstNegative(int[] arr) { for(int n : arr) { if(n < 0) return n; } return 0; } returns immediately when first negative found, stopping loop early.

2. Step 2: Verify correct fallback return

   If no negative found, method returns 0 after loop finishes, correctly.

3. Step 3: Identify flaws in other options

   public static int firstNegative(int[] arr) { for(int n : arr) { if(n < 0) return n; else return 0; } } returns 0 too early inside loop. public static int firstNegative(int[] arr) { int result = 0; for(int n : arr) { if(n < 0) result = n; } return result; } updates result but does not return early. public static int firstNegative(int[] arr) { for(int n : arr) { if(n < 0) break; } return 0; } breaks loop but always returns 0, ignoring negatives.

4. Final Answer:

   public static int firstNegative(int[] arr) { for(int n : arr) { if(n < 0) return n; } return 0; } -> Option A

5. Quick Check:

   Return inside loop for first match, fallback after loop [OK]

Hint: Return immediately on first match, fallback after loop ends [OK]

Common Mistakes:

• Returning fallback inside loop too early
• Not returning immediately on first match
• Using break without return causing wrong output