Return inside loops in C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

C

int first_even(int arr[], int size) {
    for (int i = 0; i < size; i++) {
        if (arr[i] % 2 == 0) {
            return [1];
        }
    }
    return -1;
}

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

Aarr[i]

Bi

Csize

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the index instead of the value.

Returning a constant like 0 instead of the found number.

The function returns the first even number found in the array, so it should return arr[i].

2fill in blank

medium

Complete the code to return the index of the first negative number in the array.

C

int first_negative_index(int arr[], int size) {
    for (int i = 0; i < size; i++) {
        if (arr[i] < 0) {
            return [1];
        }
    }
    return -1;
}

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

A-1

Bi

Csize

Darr[i]

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the value instead of the index.

Returning the array size or a constant.

The function should return the index where the first negative number is found, so it returns i.

3fill in blank

hard

Fix the error in the code to return the sum of positive numbers, stopping early if a zero is found.

C

int sum_positive(int arr[], int size) {
    int sum = 0;
    for (int i = 0; i < size; i++) {
        if (arr[i] == 0) {
            [1];
        }
        if (arr[i] > 0) {
            sum += arr[i];
        }
    }
    return sum;
}

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

Abreak

Bcontinue

Creturn sum

Dreturn 0

Attempts:

3 left

💡 Hint

Common Mistakes

Using break instead of return, which only exits the loop but not the function.

Using continue, which skips the current iteration but does not stop.

When zero is found, the function should return the current sum immediately, so use return sum;.

4fill in blank

hard

Fill both blanks to return the first number greater than 10 and its index.

C

int* first_greater_than_ten(int arr[], int size) {
    static int result[2];
    for (int i = 0; i < size; i++) {
        if (arr[i] [1] 10) {
            result[0] = arr[i];
            result[1] = [2];
            return result;
        }
    }
    return NULL;
}

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

A>

B<

Ci

Darr[i]

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator.

Storing the value instead of the index in the second result element.

The condition should check if the number is greater than 10 using >, and the index i is stored as the second element.

5fill in blank

hard

Fill all three blanks to return the first negative number, its index, and stop the loop.

C

int find_negative(int arr[], int size, int *index) {
    for (int i = 0; i < size; i++) {
        if (arr[i] [1] 0) {
            *index = [2];
            [3] arr[i];
        }
    }
    *index = -1;
    return 0;
}

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

A<

Bi

Creturn

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators.

Not returning immediately, causing wrong results.

The condition checks if the number is less than zero using <. The index is set to i, and the function returns the found negative number immediately with return.

Practice

1. What happens when a return statement is executed inside a loop in a C function?

easy

A. The program crashes due to an error.

B. The loop skips the current iteration and continues.

C. The loop finishes all iterations before returning.

D. The function immediately stops and returns the specified value.

Solution

1. Step 1: Understand the role of return inside a function

   The return statement immediately ends the function and sends back a value.

2. Step 2: Effect of return inside a loop

   When return is inside a loop, the function stops as soon as return is executed, even if the loop is not finished.

3. Final Answer:

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

4. Quick Check:

   Return inside loop = immediate function exit [OK]

Hint: Return inside loop stops function immediately [OK]

Common Mistakes:

• Thinking return only exits the loop, not the function
• Assuming loop completes before return
• Confusing return with continue or break

2. Which of the following is the correct syntax to return the value 5 inside a for loop in C?

easy

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

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

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

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

Solution

1. Step 1: Check syntax of return statement

   Return must be followed by a value and a semicolon inside braces if used.

2. Step 2: Analyze each option

   for(int i=0; i<3; i++) { return 5; } uses correct syntax with braces and semicolon. for(int i=0; i<3; i++) return(5) misses semicolon, invalid. for(int i=0; i<3; i++) { return; 5; } has return without value then 5; which is invalid. for(int i=0; i<3; i++) { return 5 } misses semicolon after return 5.

3. Final Answer:

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

4. Quick Check:

   Return syntax needs value and semicolon [OK]

Hint: Return must have value and semicolon inside braces [OK]

Common Mistakes:

• Omitting semicolon after return
• Placing code after return on same line
• Using return without value in non-void function

3. What is the output of this C function?

int findFirstEven(int arr[], int size) {
  for(int i = 0; i < size; i++) {
    if(arr[i] % 2 == 0) {
      return arr[i];
    }
  }
  return -1;
}

int main() {
  int nums[] = {3, 7, 8, 5};
  printf("%d", findFirstEven(nums, 4));
  return 0;
}

medium

A. 3

B. 7

C. 8

D. -1

Solution

1. Step 1: Trace the loop to find first even number

   The array is {3, 7, 8, 5}. Loop checks each element: 3 (odd), 7 (odd), 8 (even).

2. Step 2: Return when first even found

   At element 8, condition is true, so function returns 8 immediately, skipping rest.

3. Final Answer:

   8 -> Option C

4. Quick Check:

   Return stops loop at first even number 8 [OK]

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

Common Mistakes:

• Assuming loop continues after return
• Returning wrong element index
• Confusing return value with loop index

4. Identify the error in this C function that tries to return the first negative number from an array:

int firstNegative(int arr[], int n) {
  for(int i=0; i

medium

A. The function has no return statement.

B. The function returns 0 too early, skipping rest of array.

C. The loop syntax is incorrect.

D. The function returns negative numbers incorrectly.

Solution

1. Step 1: Analyze the loop and return logic

   The else clause returns 0 immediately if the first element is not negative, so the loop never checks further elements.

2. Step 2: Understand why this is a problem

   This causes the function to stop early and miss negative numbers later in the array.

3. Final Answer:

   The function returns 0 too early, skipping rest of array. -> Option B

4. Quick Check:

   Return in else exits function too soon [OK]

Hint: Avoid return in else inside loop to check all elements [OK]

Common Mistakes:

• Returning inside else causes early exit
• Not using braces causing confusion
• Assuming loop checks all elements

5. You want to write a C function that returns the index of the first prime number in an array, or -1 if none found. Which code snippet correctly uses return inside a loop to achieve this?

hard

A. for(int i=0; i

B. for(int i=0; i

C. for(int i=0; i

D. for(int i=0; i

Solution

1. Step 1: Understand the goal

   We want to return the index of the first prime number found, or -1 if none.

2. Step 2: Analyze each option's logic

   for(int i=0; i

3. Final Answer:

   for(int i=0; i -> Option A

4. Quick Check:

   Return index on first prime, else -1 after loop [OK]

Hint: Return inside loop on condition, return default after loop [OK]

Common Mistakes:

• Returning wrong value inside loop
• Using break without return
• Returning default inside loop