Return values in Go - Mini Project: Build & Apply

Return values

📖 Scenario: You are creating a simple calculator program in Go. You want to write a function that adds two numbers and returns the result.

🎯 Goal: Build a Go program with a function that takes two numbers, adds them, and returns the sum. Then print the returned result.

📋 What You'll Learn

Create a function called add that takes two int parameters and returns an int

Call the add function with two numbers

Store the returned value in a variable

Print the stored 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 writing reusable code and building programs that perform tasks and give back results.

1

Create the add function

Write a function called add that takes two int parameters named a and b and returns their sum as an int. The function should return a + b.

Go

package main

func add(a int, b int) int {
    // Your code here
}

func main() {

}

Hint

Use the return keyword to send back the sum of a and b.

2

Call the add function and store the result

Inside the main function, call the add function with the numbers 5 and 7. Store the returned value in a variable called result.

Go

package main

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

func main() {
    // Your code here
}

Hint

Use := to declare and assign result in one step.

3

Print the result

Add a fmt.Println statement inside main to print the value stored in result. Remember to import the fmt package at the top.

Go

package main

import "fmt"

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

func main() {
    result := add(5, 7)
    // Your code here
}

Hint

Use fmt.Println(result) to show the sum on the screen.

4

Run the program to see the output

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

Go

package main

import "fmt"

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

func main() {
    result := add(5, 7)
    fmt.Println(result)
    // Your code here
}

Hint

Check the terminal or console output. It should show 12.

Practice

1. What does a function's return value in Go do?

easy

A. It defines the function's name.

B. It comments the code for documentation.

C. It declares variables inside the function.

D. It sends a result back to the place where the function was called.

Solution

1. Step 1: Understand the purpose of return values

   Return values are used to send results from a function back to the caller.

2. Step 2: Identify the correct description

   Only It sends a result back to the place where the function was called. correctly describes this purpose.

3. Final Answer:

   It sends a result back to the place where the function was called. -> Option D

4. Quick Check:

   Return value = sends result back [OK]

Hint: Return values send results back to the caller [OK]

Common Mistakes:

• Confusing return values with variable declarations
• Thinking return values name the function
• Assuming return values are comments

2. Which of the following is the correct way to declare a function in Go that returns an integer?

easy

A. func add() int { return 5 }

B. func add() { return 5 }

C. func add int() { return 5 }

D. func add() int return 5

Solution

1. Step 1: Check function syntax for return type

   In Go, the return type is specified after parentheses: func name() type { ... }

2. Step 2: Verify each option

   func add() int { return 5 } correctly declares a function returning int. Others have syntax errors.

3. Final Answer:

   func add() int { return 5 } -> Option A

4. Quick Check:

   Return type after () = int [OK]

Hint: Return type goes after parentheses in function declaration [OK]

Common Mistakes:

• Placing return type before function name
• Omitting return type when returning a value
• Incorrect function syntax

3. What is the output of this Go code?

func multiply(a, b int) int {
    return a * b
}

func main() {
    result := multiply(3, 4)
    fmt.Println(result)
}

medium

A. 7

B. 34

C. Error: missing import

D. 12

Solution

1. Step 1: Check for required imports

   The code uses fmt.Println(result) but lacks import "fmt", causing a compile error: undefined fmt.

2. Step 2: Verify function logic

   The multiply function correctly computes 3*4=12, but the program won't compile or run without the import.

3. Final Answer:

   Error: missing import -> Option C

4. Quick Check:

   fmt.Println needs import "fmt" [OK]

Hint: fmt.Println requires import "fmt" [OK]

Common Mistakes:

• Forgetting import "fmt"
• Computing 3*4=12 but ignoring missing import
• Assuming code runs without imports

4. Identify the error in this Go function that returns two integers:

func divide(a, b int) (int, int) {
    return a / b
}

medium

A. Division operator is incorrect.

B. Function returns only one value but declares two return types.

C. Function parameters are missing types.

D. Function name is invalid.

Solution

1. Step 1: Check return type declaration

   The function declares two return values (int, int) but returns only one value.

2. Step 2: Identify mismatch in return statement

   Returning a single value causes a compile error because two values are expected.

3. Final Answer:

   Function returns only one value but declares two return types. -> Option B

4. Quick Check:

   Return count must match declared types [OK]

Hint: Return values count must match declared types [OK]

Common Mistakes:

• Returning fewer values than declared
• Wrong operator usage confusion
• Ignoring function signature

5. How can you write a Go function that returns both the sum and product of two integers?

hard

A. func calc(a, b int) (int, int) { return a+b, a*b }

B. func calc(a, b int) int { return a+b, a*b }

C. func calc(a, b int) (int) { return a+b, a*b }

D. func calc(a, b int) (int, int) { return a+b + a*b }

Solution

1. Step 1: Define function with two return types

   The function must declare two return types (int, int) for sum and product.

2. Step 2: Return sum and product as two values

   Return both values separated by a comma: return a+b, a*b.

3. Final Answer:

   func calc(a, b int) (int, int) { return a+b, a*b } -> Option A

4. Quick Check:

   Two return values with matching types [OK]

Hint: Return multiple values separated by commas [OK]

Common Mistakes:

• Returning multiple values with single return type
• Returning combined expression instead of two values
• Incorrect return type syntax