Return values in C++ - Step-by-Step Execution

Concept Flow - Return values

Function called

↓

Execute function body

↓

Return value computed

↓

Return value sent back

↓

Use returned value in caller

When a function finishes, it sends back a value to where it was called, which can then be used.

Execution Sample

C++

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

int main() {
    int result = add(3, 4);
    return 0;
}

This code defines a function that adds two numbers and returns the sum, which is stored in 'result'.

Execution Table

Step	Action	Variables	Return Value	Notes
1	Call add(3, 4)	a=3, b=4	N/A	Function starts with parameters 3 and 4
2	Calculate a + b	a=3, b=4	7	Sum is 7
3	Return 7 to caller	a=3, b=4	7	Function ends, returns 7
4	Assign return value to result	result=7	N/A	Main stores 7 in result
5	End of main	result=7	N/A	Program ends

💡 Function returns value 7, assigned to result, then program ends

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
a	N/A	3	3	3	N/A	N/A
b	N/A	4	4	4	N/A	N/A
result	N/A	N/A	N/A	N/A	7	7

Key Moments - 3 Insights

Why does the function stop executing after the return statement?

Because the return statement sends the value back and immediately ends the function, as shown in step 3 of the execution_table.

What happens to the variables inside the function after it returns?

They are discarded after the function ends, so 'a' and 'b' exist only during the function call (steps 1-3).

How does the returned value get used in the main function?

The returned value 7 is assigned to 'result' in step 4, so main can use it after the function call.

Visual Quiz - 3 Questions

Look at the execution_table, what is the return value at step 2?

A 3

B 4

C 7

D N/A

💡 Hint

Check the 'Return Value' column at step 2 in the execution_table.

At which step does the function end and return the value?

A Step 1

B Step 3

C Step 4

D Step 5

💡 Hint

Look for the step where the 'Return Value' is sent back and function ends in the execution_table.

If the return statement was missing, what would happen to 'result' in main?

A result would be uninitialized or garbage

B result would be assigned 7 anyway

C result would be assigned 0

D Program would not compile

💡 Hint

Think about what happens if a function does not return a value but main expects one.

Concept Snapshot

Return values in C++:
- Use 'return' to send a value back from a function.
- Function ends immediately after 'return'.
- Caller receives the returned value to use.
- Variables inside function exist only during call.
- Returned value can be stored or used directly.

Full Transcript

This example shows how a function in C++ returns a value. The function 'add' takes two numbers, adds them, and returns the sum. When 'add(3, 4)' is called, the function runs with a=3 and b=4. It calculates 3+4=7, then returns 7. The main function receives this 7 and stores it in 'result'. The return statement ends the function immediately. Variables inside the function exist only during the call. The returned value is used by the caller after the function ends.