Using return codes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a return code in C programming?

A return code is an integer value that a function returns to indicate success or failure of its execution. It helps the calling code understand what happened inside the function.

beginner

Why do we use return codes instead of printing error messages directly inside functions?

Using return codes lets the calling function decide how to handle errors, making the program more flexible and easier to maintain. It separates error detection from error handling.

beginner

What does a return code of 0 usually mean in C programs?

A return code of 0 usually means the function or program completed successfully without errors.

beginner

How can you check a function's return code in C?

You can store the return value in a variable and use an if statement to check it. For example:

int result = myFunction();
if (result != 0) {
  // handle error
}

beginner

Give an example of a simple C function that uses return codes to indicate success or failure.

int divide(int a, int b, int *result) {
  if (b == 0) return -1; // error: division by zero
  *result = a / b;
  return 0; // success
}

What does a return code of 0 usually indicate in C?

A Unknown

B Failure

C Warning

D Success

In C, a return code of 0 typically means the function or program ran successfully without errors.

How should a calling function handle a non-zero return code?

A Ignore it

B Treat it as an error and handle accordingly

C Always print a success message

D Restart the program automatically

A non-zero return code usually signals an error, so the calling function should handle it properly.

Which of these is a good reason to use return codes?

A To avoid writing functions

B To make the program run faster

C To separate error detection from error handling

D To print messages automatically

Return codes help separate detecting errors from deciding what to do about them.

What type of value is a return code in C?

A int

B float

C char

D string

Return codes are usually integers (int) in C.

If a function returns -1 as a return code, what does it usually mean?

A Error or failure

B No operation

C Success

D Function is still running

Negative return codes like -1 often indicate an error or failure.

Explain what return codes are and why they are useful in C programming.

Think about how functions tell the rest of the program if they worked or not.

Describe how you would check and handle a return code from a function in C.

Consider a simple if condition after calling a function.

Practice

1. What does a return code of 0 usually mean in C functions?

easy

A. The function completed successfully

B. The function encountered an error

C. The function did not run

D. The function returned a pointer

Solution

1. Step 1: Understand return codes meaning

   In C, a return code of 0 typically means success or no error.

2. Step 2: Interpret the code 0

   Since 0 means success, the function completed its task without problems.

3. Final Answer:

   The function completed successfully -> Option A

4. Quick Check:

   Return code 0 = success [OK]

Hint: Remember: 0 means success, non-zero means error [OK]

Common Mistakes:

• Thinking 0 means error
• Confusing return code with function output
• Assuming non-zero means success

2. Which of the following is the correct way to return an error code from a C function?

easy

A. return 0;

B. return 'error';

C. return -1;

D. return true;

Solution

1. Step 1: Identify valid return types for error codes

   Return codes are integers, so returning a number like -1 is valid for error.

2. Step 2: Check each option

   return 0; returns 0 (success), B returns a multi-char constant (invalid), C returns true (boolean, invalid in C), D returns -1 (valid error code).

3. Final Answer:

   return -1; -> Option C

4. Quick Check:

   Use integer codes for errors [OK]

Hint: Return integer codes; negative often means error [OK]

Common Mistakes:

• Returning strings instead of integers
• Using boolean values in C return codes
• Returning 0 for errors

3. What will be the output of this C program?

#include <stdio.h>
int check(int x) {
    if (x > 0) return 0;
    else return 1;
}
int main() {
    int result = check(-5);
    printf("Return code: %d\n", result);
    return 0;
}

medium

A. Return code: 1

B. Return code: -5

C. Return code: 0

D. No output

Solution

1. Step 1: Analyze the check function behavior

   If x > 0, it returns 0; otherwise, it returns 1.

2. Step 2: Apply input value -5

   Since -5 is not greater than 0, the function returns 1.

3. Final Answer:

   Return code: 1 -> Option A

4. Quick Check:

   Input -5 <= 0, so return 1 [OK]

Hint: Check conditions carefully to find returned code [OK]

Common Mistakes:

• Assuming negative input returns 0
• Confusing return value with input
• Ignoring else branch

4. Identify the error in this C function that uses return codes:

int process(int val) {
    if (val == 0)
        return 0;
    else
        return;
}

medium

A. Using 0 as success code

B. No error, code is correct

C. Function should return void

D. Missing return value in else branch

Solution

1. Step 1: Check function return type and return statements

   The function returns int, so every return must have an int value.

2. Step 2: Identify missing return value

   The else branch has 'return;' without a value, which is invalid for int return type.

3. Final Answer:

   Missing return value in else branch -> Option D

4. Quick Check:

   int functions must return int always [OK]

Hint: Every return in int function must return int value [OK]

Common Mistakes:

• Returning nothing in non-void function
• Confusing void and int return types
• Ignoring compiler warnings

5. You want to write a function int saveData() that returns 0 on success, 1 if file not found, and 2 if write error. Which is the best way to handle these return codes in main()?

hard

A. Ignore the return code and always print "Success"

B. Check if return code is 0, else print error message based on code

C. Return the code from main without checking

D. Use return codes only for debugging, not in main

Solution

1. Step 1: Understand return codes purpose

   Return codes help main know if saveData succeeded or failed and why.

2. Step 2: Choose proper handling in main

   Main should check if return code is 0 (success), else print specific error messages for 1 or 2.

3. Final Answer:

   Check if return code is 0, else print error message based on code -> Option B

4. Quick Check:

   Use return codes to handle errors clearly [OK]

Hint: Check return codes to handle errors clearly [OK]

Common Mistakes:

• Ignoring return codes in main
• Printing success without checking
• Using return codes only for debugging