Return values in C++ - Mini Project: Build & Apply

Return values

📖 Scenario: Imagine you are creating a simple calculator program that adds two numbers and returns the result.

🎯 Goal: Build a program that defines a function to add two numbers and returns the sum. Then, use this function to get the result and display it.

📋 What You'll Learn

Create a function called add that takes two integers as parameters

The add function must return the sum of the two integers

Call the add function with the numbers 7 and 5

Store the returned value in a variable called result

Print the value of result

💡 Why This Matters

🌍 Real World

Functions that return values are used everywhere in programming to get results from calculations or data processing.

💼 Career

Understanding return values is essential for software development jobs, as it helps you write clear and reusable code.

1

Create the add function

Write a function called add that takes two integers named a and b and returns their sum.

C++

#include 

// Write the add function here

int main() {
    return 0;
}

Hint

Define a function with return type int named add that returns a + b.

2

Call the add function and store the result

Inside the main function, call the add function with arguments 7 and 5 and store the returned value in an integer variable called result.

C++

#include 

int add(int a, int b) {
    return a + b;
}

int main() {
    // Call add with 7 and 5 and store in result
    
    return 0;
}

Hint

Use int result = add(7, 5); inside main.

3

Print the result

Add a line inside main to print the value of result using std::cout.

C++

#include 

int add(int a, int b) {
    return a + b;
}

int main() {
    int result = add(7, 5);
    // Print the result
    
    return 0;
}

Hint

Use std::cout << result << std::endl; to print the value.

4

Run the program and see the output

Run the program. It should print the sum of 7 and 5, which is 12.

C++

#include 

int add(int a, int b) {
    return a + b;
}

int main() {
    int result = add(7, 5);
    std::cout << result << std::endl;
    return 0;
}

// Run the program to see the output

Hint

The program should print 12 because 7 + 5 = 12.

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