Function calling - Step-by-Step Execution

Concept Flow - Function calling

Start main()

↓

Call function foo()

↓

Execute foo() body

↓

Return from foo()

↓

Continue main()

↓

End main()

The program starts in main(), calls another function, runs that function's code, then returns to main() to finish.

Execution Sample

C

int foo() {
    return 5;
}

int main() {
    int x = foo();
    return 0;
}

Calls function foo() from main(), foo() returns 5, which is stored in x.

Execution Table

Step	Function	Action	Variable Changes	Return Value
1	main	Start main()	x: uninitialized	N/A
2	main	Call foo()	x: uninitialized	N/A
3	foo	Execute return 5;	N/A	5
4	main	Assign foo() return to x	x: 5	N/A
5	main	Return 0 and end	x: 5	0

💡 main() returns 0, program ends

Variable Tracker

Variable	Start	After Step 4	Final
x	uninitialized	5	5

Key Moments - 3 Insights

Why does the program jump to foo() when main() calls it?

When main() calls foo() (see Step 2 in execution_table), the program pauses main() and runs foo() code next.

How does the value 5 get back to main()?

foo() returns 5 (Step 3), which main() receives and stores in x (Step 4).

What happens after foo() finishes?

After foo() returns, the program continues running main() from where it left off (Step 4).

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of x after Step 4?

A uninitialized

B 0

C 5

D N/A

💡 Hint

Check the 'Variable Changes' column at Step 4 in execution_table.

At which step does foo() return a value to main()?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look for the step where 'Return Value' is 5 in execution_table.

If foo() returned 10 instead of 5, what would x be after Step 4?

A 10

B 5

C 0

D uninitialized

💡 Hint

Variable x gets the return value from foo() as shown in variable_tracker and execution_table.

Concept Snapshot

Function calling in C:
- main() starts program
- main() calls another function by name
- Program jumps to called function
- Called function runs and returns value
- Program resumes main() with returned value
- Use return to send data back

Full Transcript

This example shows how a function call works in C. The program starts in main(). When main() calls foo(), the program pauses main() and runs foo() code. foo() returns a value (5), which main() receives and stores in variable x. After foo() finishes, the program continues running main() from where it left off. This process lets us organize code into reusable parts and pass data between them.