Return inside loops in Go - Step-by-Step Execution

Concept Flow - Return inside loops

Start function

↓

Enter loop

↓

Check condition

Yes↓

Execute loop body

↓

Return encountered?

Yes→Exit function immediately

No↓

Next iteration

Back to Check condition↓

Exit loop

↓

Return at end of function

↓

End function

↩Back to Check condition

The function starts and enters a loop. Each iteration checks a condition. If a return statement runs inside the loop, the function exits immediately, skipping remaining iterations.

Execution Sample

Go

func findFirstEven(nums []int) int {
    for _, n := range nums {
        if n%2 == 0 {
            return n
        }
    }
    return -1
}

This function loops through numbers and returns the first even number it finds, stopping the loop immediately.

Execution Table

Step	Iteration	Current number (n)	Condition (n%2==0)	Action	Return Value
1	1	3	false	Continue loop	none
2	2	7	false	Continue loop	none
3	3	4	true	Return 4 and exit function	4

💡 Return executed at iteration 3 when n=4, function exits immediately.

Variable Tracker

Variable	Start	After 1	After 2	After 3 (Return)
n	undefined	3	7	4
return value	none	none	none	4

Key Moments - 2 Insights

Why does the loop stop immediately when return is executed inside it?

Because return exits the entire function immediately, skipping all remaining loop iterations as shown in execution_table row 3.

What happens if no number satisfies the condition inside the loop?

The loop finishes all iterations without returning, then the function returns the value after the loop, here -1 (not shown in this trace).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'n' at step 2?

A 4

B 3

C 7

D none

💡 Hint

Check the 'Current number (n)' column at step 2 in the execution_table.

At which iteration does the function return a value?

A 3

B 2

C 1

D Never

💡 Hint

Look at the 'Return Value' column and find when it changes from 'none' to a number.

If the input slice had no even numbers, what would happen to the return value?

A Return the first number anyway

B Return -1 after the loop finishes

C Return 0 immediately

D The function would never return

💡 Hint

Refer to the code in execution_sample where return -1 is after the loop.

Concept Snapshot

Return inside loops in Go:
- A return inside a loop exits the entire function immediately.
- Loop stops running once return executes.
- If no return in loop, function can return after loop.
- Useful to find and return first matching item quickly.

Full Transcript

This example shows a Go function that loops through a list of numbers. Each number is checked if it is even. When the function finds the first even number, it returns that number immediately, stopping the loop and the function. If no even number is found, the function returns -1 after the loop finishes. The execution table traces each step, showing the current number, condition check, and when the return happens. The variable tracker shows how the variable 'n' changes each iteration and when the return value is set. Key moments clarify why the loop stops on return and what happens if no return occurs inside the loop. The quiz tests understanding of these steps and outcomes.