Return values in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a return value in C++?

A return value is the result a function sends back to the part of the program that called it. It lets the function give information after finishing its task.

beginner

How do you specify the type of a return value in a C++ function?

You write the type before the function name. For example, int means the function returns an integer number.

intermediate

What happens if a function has a return type but no return statement?

If a function promises to return a value but does not use return, the program may behave unpredictably or cause an error.

intermediate

Can a function return multiple values directly in C++?

No, a function returns only one value directly. To return multiple values, you can use structures, classes, or output parameters.

beginner

What does the void return type mean?

It means the function does not return any value. It just performs actions without sending back a result.

What keyword is used to send a value back from a function in C++?

A return

B send

C output

D yield

The return keyword is used to send a value back from a function.

If a function is declared as int add(), what must it do?

A Return a string

B Return nothing

C Return an integer value

D Print output only

The function must return an integer value because its return type is int.

What is the return type of a function that does not return any value?

A int

B void

C null

D none

The void return type means the function returns no value.

Which of these can a C++ function return directly?

A One value

B Multiple values

C No values and multiple values

D Multiple values without any container

A function can return only one value directly.

What happens if a function with a non-void return type does not have a return statement?

A Returns zero automatically

B Returns a default string

C Returns void

D Undefined behavior or error

Not returning a value when expected causes undefined behavior or errors.

Explain what a return value is and why it is important in C++ functions.

Think about how functions share results with the rest of the program.

Describe how to handle returning multiple pieces of information from a C++ function.

Consider containers or references to send back more than one value.

Practice

1. What does the return statement do in a C++ function?

easy

A. It sends a value back to the place where the function was called.

B. It prints a value to the screen.

C. It declares a new variable inside the function.

D. It ends the program immediately.

Solution

1. Step 1: Understand the purpose of return

   The return statement is used to send a value from a function back to the caller.

2. Step 2: Differentiate from other statements

   Printing to screen or declaring variables are different actions; return specifically sends a value back.

3. Final Answer:

   It sends a value back to the place where the function was called. -> Option A

4. Quick Check:

   Return sends value back [OK]

Hint: Remember: return sends value back to caller [OK]

Common Mistakes:

• Confusing return with printing output
• Thinking return declares variables
• Believing return ends the whole program

2. Which of the following is the correct syntax to return an integer value 5 from a function in C++?

easy

A. return = 5;

B. return(5)

C. return 5;

D. return: 5;

Solution

1. Step 1: Recall correct return syntax

   In C++, the correct way to return a value is return value; with a semicolon.

2. Step 2: Check each option

   return 5; uses return 5; which is correct. return(5) misses semicolon. Options C and D use invalid syntax.

3. Final Answer:

   return 5; -> Option C

4. Quick Check:

   Correct return syntax ends with semicolon [OK]

Hint: Use 'return value;' with semicolon [OK]

Common Mistakes:

• Omitting semicolon after return
• Using '=' with return
• Using colon ':' instead of semicolon

3. What will be the output of the following code?

int add() {
  return 2 + 3;
}

int main() {
  int result = add();
  std::cout << result;
  return 0;
}

medium

A. 23

B. 5

C. 0

D. Compilation error

Solution

1. Step 1: Analyze the add() function

   The function returns the sum of 2 + 3, which is 5.

2. Step 2: Check main() output

   Main calls add(), stores 5 in result, then prints it using std::cout.

3. Final Answer:

   5 -> Option B

4. Quick Check:

   2 + 3 = 5 [OK]

Hint: Add inside return, then print result [OK]

Common Mistakes:

• Thinking return concatenates numbers
• Confusing return value with print output
• Expecting zero without calculation

4. Identify the error in this function and choose the correct fix:

int multiply(int a, int b) {
  a * b;
}

medium

A. Add return before a * b;

B. Change function return type to void

C. Add semicolon after function declaration

D. Replace a * b; with return a + b;

Solution

1. Step 1: Check function body

   The function calculates a * b; but does not return it.

2. Step 2: Fix missing return

   To return the product, add return before a * b;.

3. Final Answer:

   Add return before a * b; -> Option A

4. Quick Check:

   Function must return value if return type is int [OK]

Hint: Return the calculated value explicitly [OK]

Common Mistakes:

• Forgetting to use return statement
• Changing return type unnecessarily
• Confusing multiplication with addition

5. You want a function that returns the larger of two integers. Which of these implementations correctly returns the larger value?

hard

A. int max(int x, int y) { return; }

B. int max(int x, int y) { if (x > y) return y; else return x; }

C. int max(int x, int y) { return x + y; }

D. int max(int x, int y) { if (x > y) return x; else return y; }

Solution

1. Step 1: Understand the goal

   The function should return the larger of x and y.

2. Step 2: Check each option logic

   int max(int x, int y) { if (x > y) return x; else return y; } returns x if x > y, else y, which is correct. int max(int x, int y) { if (x > y) return y; else return x; } reverses logic. int max(int x, int y) { return x + y; } returns sum, not max. int max(int x, int y) { return; } returns nothing.

3. Final Answer:

   int max(int x, int y) { if (x > y) return x; else return y; } -> Option D

4. Quick Check:

   Return larger value using if-else [OK]

Hint: Return x if greater, else y [OK]

Common Mistakes:

• Swapping return values in if-else
• Returning sum instead of max
• Missing return value