Return values in Go - Step-by-Step Execution

Concept Flow - Return values

Start function call

↓

Execute function body

↓

Return value(s)

↓

Receive returned value(s)

↓

Continue program

This flow shows how a function runs, sends back value(s), and the program uses them.

Execution Sample

Go

package main
import "fmt"
func add(a, b int) int {
    return a + b
}
func main() {
    fmt.Println(add(3, 4))
}

This code defines a function that adds two numbers and returns the sum, then prints it.

Execution Table

Step	Action	Variables	Return Value	Output
1	Call add(3, 4)	a=3, b=4
2	Calculate a + b	a=3, b=4	7
3	Return 7 to caller	a=3, b=4	7
4	Print returned value			7
5	Program ends

💡 Function returns value 7, printed by main, then program ends

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
a	-	3	3	3
b	-	4	4	4
return value	-		7	7

Key Moments - 2 Insights

Why do we see the return value only after the function finishes?

Because the function runs all its code first (see Step 2), then sends back the value (Step 3). The program waits for this before printing.

What happens if the function has no return statement?

The function returns nothing (void). In Go, if the function signature says it returns a value, it must have a return statement (not shown here).

Visual Quiz - 3 Questions

Look at the execution table, what is the return value at Step 3?

A 7

B 3

C 4

D 0

💡 Hint

Check the 'Return Value' column at Step 3 in the execution table.

At which step does the program print the returned value?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Output' column in the execution table to find when printing happens.

If we change add(3, 4) to add(5, 6), what will be the return value at Step 3?

A 7

B 11

C 9

D 0

💡 Hint

Return value is sum of inputs a and b, see variable values in variable_tracker.

Concept Snapshot

func functionName(params) returnType {
    // code
    return value
}

- Function runs code then returns value.
- Caller receives and can use returned value.
- Return ends function execution.

Full Transcript

This example shows how a Go function returns a value. The function add takes two numbers, adds them, and returns the sum. The program calls add(3, 4), the function runs and returns 7. Then main prints 7. The execution table traces each step: calling the function, calculating sum, returning value, printing output, and ending. Variables a and b hold inputs, return value holds the sum. Beginners often wonder why return happens after all code runs; it does because return sends the final result back to the caller. If the function had no return, it would return nothing. Changing inputs changes the return value accordingly. This is the basic flow of return values in Go functions.

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