Using return codes - Step-by-Step Execution

Concept Flow - Using return codes

Start main function

↓

Call function

↓

Function runs

↓

Function returns code

↓

Check return code

↓

End program

The program calls a function, gets a return code, then decides what to do based on that code.

Execution Sample

C

#include <stdio.h>

int checkNumber(int n) {
    if (n > 0) return 0;
    else return 1;
}

int main() {
    int result = checkNumber(-5);
    if (result == 0) printf("Positive number\n");
    else printf("Not positive\n");
    return 0;
}

This code checks if a number is positive and returns 0 if yes, 1 if no, then prints a message based on the return code.

Execution Table

Step	Action	Function Called	Input	Return Code	Condition Checked	Output
1	Start main	N/A	N/A	N/A	N/A	N/A
2	Call checkNumber	checkNumber	-5	N/A	N/A	N/A
3	Inside checkNumber	checkNumber	-5	N/A	Check if -5 > 0	No
4	Return from checkNumber	checkNumber	-5	1	N/A	N/A
5	Back in main	N/A	N/A	1	result == 0?	No
6	Print message	N/A	N/A	1	N/A	Not positive
7	End program	N/A	N/A	N/A	N/A	N/A

💡 Program ends after printing message based on return code 1 (not positive).

Variable Tracker

Variable	Start	After checkNumber call	Final
n	N/A	-5	-5
result	N/A	1	1

Key Moments - 3 Insights

Why does the function return 1 when the number is not positive?

Because in the execution_table row 3, the condition 'n > 0' is false, so the else branch returns 1 to indicate 'not positive'.

How does main know if the number is positive or not?

Main checks the return code stored in 'result' (row 5). If it is 0, it means positive; otherwise, not positive.

What happens if the function returns 0?

If return code is 0, main prints 'Positive number' as shown in the logic after row 5.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what is the return code from checkNumber?

A -5

B 0

C 1

D N/A

💡 Hint

Check the 'Return Code' column at step 4 in the execution_table.

At which step does main check if the return code means positive number?

A Step 2

B Step 5

C Step 3

D Step 6

💡 Hint

Look at the 'Condition Checked' column to find where 'result == 0?' is evaluated.

If checkNumber returned 0, what would main print?

A Positive number

B Not positive

C No output

D Error message

💡 Hint

Refer to the output in step 6 and the condition in step 5.

Concept Snapshot

Using return codes in C:
- Functions return int codes to signal status.
- 0 usually means success or OK.
- Non-zero means error or special condition.
- Main checks return code to decide next steps.
- Use if statements to handle different codes.

Full Transcript

This example shows how a C function returns a code to indicate if a number is positive. The main function calls checkNumber with -5. Inside checkNumber, it checks if the number is greater than zero. Since -5 is not, it returns 1. Back in main, the return code is checked. Because it is 1, main prints 'Not positive'. The program ends after this. This pattern helps programs communicate success or failure between functions.