Return values in C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a return value in C?

A return value is the result a function sends back to the part of the program that called it. It tells the caller what the function computed or decided.

beginner

How do you specify the return type of a function in C?

You write the type before the function name. For example, int means the function returns an integer value.

intermediate

What happens if a function in C does not have a return statement?

If the function's return type is not void, missing a return statement can cause undefined behavior because the function does not send back a proper value.

intermediate

Can a function return multiple values directly in C?

No, C functions return only one value directly. To return multiple values, you can use pointers or structures.

beginner

What is the return type of a function that does not return any value?

The return type is void. It means the function performs actions but does not send any value back.

What keyword is used to send a value back from a function in C?

A send

B return

C output

D yield

The return keyword is used to send a value back from a function.

What is the return type of a function that returns an integer?

A float

B void

C int

D char

The return type int means the function returns an integer value.

What happens if a function declared to return int does not have a return statement?

A Returns void

B Returns zero automatically

C Compiler error

D Undefined behavior

If a function declared to return int does not return a value, it causes undefined behavior.

Which return type means a function does not return any value?

A void

B int

C null

D none

The void return type means the function does not return any value.

How can a C function return multiple values?

A Using pointers or structures

B Using multiple return statements

C Using arrays as return type

D Using the return keyword multiple times

C functions can return multiple values by using pointers or structures.

Explain what a return value is and why it is important in C functions.

Think about how functions communicate results back to the caller.

Describe how to handle returning multiple values from a function in C.

Remember C functions can only return one value directly.

Practice

1. What does the return statement do in a C function?

easy

A. It sends a value back to the place where the function was called.

B. It prints a value on the screen.

C. It declares a new variable inside the function.

D. It pauses the program execution.

Solution

1. Step 1: Understand the purpose of return

   The return statement sends a value from the function back to the caller.

2. Step 2: Differentiate from other actions

   Printing, declaring variables, or pausing are not what return does.

3. Final Answer:

   It sends a value back to the place where the function was called. -> Option A

4. Quick Check:

   Return sends value back [OK]

Hint: Return sends value back to caller, not print or pause [OK]

Common Mistakes:

• Thinking return prints output
• Confusing return with variable declaration
• Assuming return pauses program

2. Which of the following is the correct syntax for a function that returns an integer in C?

easy

A. int myFunction() { return 5; }

B. void myFunction() { return 5; }

C. int myFunction() { print(5); }

D. myFunction() int { return 5; }

Solution

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

   The function declares int return type and returns an integer value 5.

2. Step 2: Identify incorrect options

   void myFunction() { return 5; } returns a value but declares void (no return). int myFunction() { print(5); } uses print which is invalid in C. myFunction() int { return 5; } has wrong syntax.

3. Final Answer:

   int myFunction() { return 5; } -> Option A

4. Quick Check:

   Return type matches returned value [OK]

Hint: Return type must match returned value type [OK]

Common Mistakes:

• Using void but returning a value
• Using print instead of return
• Wrong function syntax

3. What is the output of this C program?

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

int main() {
    int result = add(3, 4);
    printf("%d", result);
    return 0;
}

medium

A. 34

B. 7

C. 0

D. Error

Solution

1. Step 1: Understand the add function

   The function adds two integers and returns their sum.

2. Step 2: Calculate the sum of 3 and 4

   3 + 4 equals 7, which is stored in result and printed.

3. Final Answer:

   7 -> Option B

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Add returns sum; printed result is sum [OK]

Common Mistakes:

• Concatenating numbers as strings
• Confusing return with print
• Expecting zero or error output

4. Identify the error in this C function:

int multiply(int x, int y) {
    int product = x * y;
}

medium

A. Variables x and y are not declared.

B. Incorrect multiplication operator.

C. Function name should be void.

D. Missing return statement to return the product.

Solution

1. Step 1: Check function return type and body

   The function declares it returns an int but does not return any value.

2. Step 2: Identify missing return statement

   It calculates product but never returns it, causing undefined behavior.

3. Final Answer:

   Missing return statement to return the product. -> Option D

4. Quick Check:

   Return missing in non-void function [OK]

Hint: Non-void functions must return a value [OK]

Common Mistakes:

• Forgetting to return value in non-void function
• Thinking multiplication operator is wrong
• Assuming variables are undeclared

5. You want to write a function that returns the maximum of three integers. Which of the following implementations correctly returns the maximum value?

hard

A. int maxOfThree(int a, int b, int c) {
if (a > b && a > c) return a;
else if (b > a && b > c) return b;
else return c;
}

B. int maxOfThree(int a, int b, int c) {
return a > b > c ? a : b > c ? b : c;
}

C. int maxOfThree(int a, int b, int c) {
int max = a;
if (b > max) max = b;
if (c > max) max = c;
return max;
}

D. int maxOfThree(int a, int b, int c) {
if (a > b) return a;
else if (b > c) return b;
else return c;
}

Solution

1. Step 1: Analyze int maxOfThree(int a, int b, int c) { if (a > b && a > c) return a; else if (b > a && b > c) return b; else return c; } logic

   This version correctly checks if b is greater than both a and c in the else-if condition, fixing the missing cases in the original version.

2. Step 2: Analyze int maxOfThree(int a, int b, int c) { int max = a; if (b > max) max = b; if (c > max) max = c; return max; } logic

   This compares all values step-by-step and returns the correct maximum.

3. Step 3: Analyze options C and D

   int maxOfThree(int a, int b, int c) { return a > b > c ? a : b > c ? b : c; } uses invalid chained comparison. int maxOfThree(int a, int b, int c) { if (a > b) return a; else if (b > c) return b; else return c; } misses some cases like when a is not greater than b but b is not greater than c.

4. Final Answer:

   int maxOfThree(int a, int b, int c) { int max = a; if (b > max) max = b; if (c > max) max = c; return max; } -> Option C

5. Quick Check:

   Stepwise max update returns correct max [OK]

Hint: Compare stepwise and return max variable [OK]

Common Mistakes:

• Using chained comparisons incorrectly
• Missing some comparison cases
• Returning before checking all values