Return values in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a return value in Go functions?

A return value is the output that a function sends back to the place where it was called. It lets the function give back a result after doing its work.

beginner

How do you declare a function in Go that returns an integer?

You write the function with the return type after the parameter list. For example:

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

This function returns an int.

intermediate

Can a Go function return multiple values? Give an example.

Yes, Go functions can return multiple values. For example:

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

This returns both quotient and remainder.

intermediate

What happens if a Go function does not have a return statement but declares a return type?

The Go compiler will give an error because the function promises to return a value but does not. Every path must return a value if a return type is declared.

advanced

Explain named return values in Go functions.

Named return values let you name the results in the function signature. Inside the function, you can set these names like variables and use a bare return to send them back. Example:<pre>func sumAndDiff(a, b int) (sum int, diff int) { sum = a + b; diff = a - b; return }</pre>

What does this Go function return?

func greet() string { return "Hello" }

A A string

B An integer

C Nothing

D A boolean

The function returns a string "Hello" as declared by the return type string.

How many values does this function return?

func values() (int, string) { return 5, "Go" }

A One

B Zero

C Three

D Two

The function returns two values: an int and a string.

What will happen if a function declares a return type but has no return statement?

A It compiles fine

B It causes a compile-time error

C It returns zero by default

D It returns nil

Go requires all functions with return types to have return statements; otherwise, it causes a compile-time error.

Which keyword is used to send back values from a Go function?

A return

B send

C yield

D output

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

What is special about named return values in Go?

A They are deprecated

B They require explicit return values every time

C They allow returning values without specifying them in the return statement

D They are only used for error handling

Named return values let you set variables inside the function and use a bare return without specifying values explicitly.

Explain how return values work in Go functions and how to declare them.

Think about how functions send back results after running.

Describe named return values in Go and how they simplify returning multiple results.

It's like giving names to the boxes you will send back.

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