Function calling - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a function call in C?

A function call is when you ask a function to run its code by using its name followed by parentheses, optionally with arguments inside.

beginner

How do you call a function named printMessage in C?

You call it by writing printMessage(); with parentheses and a semicolon.

beginner

What happens if you call a function without the required arguments?

The program will give an error because the function expects certain inputs to work properly.

beginner

Why do we use function calls in a program?

Function calls let us reuse code, keep programs organized, and make the program easier to read and maintain.

intermediate

What is the difference between a function declaration and a function call?

A function declaration tells the program what the function looks like. A function call actually runs the function's code.

How do you call a function named sum that takes two integers in C?

A sum(5, 10);

B int sum(5, 10);

C call sum(5, 10);

D function sum(5, 10);

To call a function, just write its name with arguments inside parentheses followed by a semicolon.

What does a function call do?

A Comments out the function

B Runs the code inside the function

C Deletes the function

D Defines the function

A function call runs the code inside the function.

Which of these is a correct function call in C?

A myFunction();

B myFunction;

C myFunction()

D call myFunction();

A function call must have parentheses and end with a semicolon.

What happens if you forget parentheses when calling a function?

A The function runs normally

B The program skips the function

C The function is declared again

D You get a syntax error

Parentheses are required to call a function; missing them causes a syntax error.

Why do we pass arguments in a function call?

A To stop the function

B To name the function

C To give the function data it needs

D To declare the function

Arguments provide the function with the data it needs to work.

Explain in your own words what a function call is and why it is important in C programming.

Think about how you ask a friend to do something for you.

Describe the syntax of calling a function with and without arguments in C.

Remember the example: printMessage(); or sum(5, 10);

Practice

1. What does it mean to call a function in C?

easy

A. Execute the code inside the function by using its name and parentheses

B. Define the function with its code block

C. Declare the function prototype

D. Write comments about the function

Solution

1. Step 1: Understand function calling

   Calling a function means running the code inside it by using its name followed by parentheses.

2. Step 2: Differentiate from defining or declaring

   Defining or declaring a function is writing it, not running it. Calling is executing it.

3. Final Answer:

   Execute the code inside the function by using its name and parentheses -> Option A

4. Quick Check:

   Function call = run code by name() [OK]

Hint: Calling means running code by writing functionName() [OK]

Common Mistakes:

• Confusing calling with defining the function
• Thinking calling means declaring the function prototype
• Believing calling is writing comments

2. Which of the following is the correct syntax to call a function named printMessage in C?

easy

A. printMessage();

B. call printMessage;

C. printMessage;

D. function printMessage();

Solution

1. Step 1: Recall function call syntax

   In C, calling a function requires its name followed by parentheses and a semicolon.

2. Step 2: Check each option

   printMessage(); uses correct syntax: function name + parentheses + semicolon. Others are invalid syntax.

3. Final Answer:

   printMessage(); -> Option A

4. Quick Check:

   Function call syntax = name() [OK]

Hint: Function call always ends with (); [OK]

Common Mistakes:

• Omitting parentheses when calling
• Using keywords like 'call' which don't exist in C
• Missing semicolon at the end

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

void greet() {
    printf("Hello!\n");
}

int main() {
    greet();
    return 0;
}

medium

A. Compilation error

B. Hello!

C. No output

D. greet()

Solution

1. Step 1: Understand function greet()

   The function greet() prints "Hello!" followed by a newline.

2. Step 2: Check main() function call

   Main calls greet(), so the program prints "Hello!" on the screen.

3. Final Answer:

   Hello! -> Option B

4. Quick Check:

   Calling greet() prints Hello! [OK]

Hint: Calling greet() prints its message exactly [OK]

Common Mistakes:

• Thinking function name prints output
• Assuming no output without explicit main print
• Confusing function call with declaration

4. Identify the error in this code snippet:

void sayHi() {
    printf("Hi!\n");
}

int main() {
    sayHi;
    return 0;
}

medium

A. printf statement is incorrect

B. Missing semicolon after sayHi

C. Function sayHi is not declared

D. Missing parentheses when calling sayHi

Solution

1. Step 1: Check function call syntax

   In main(), sayHi is written without parentheses, so it is not a function call.

2. Step 2: Correct function call

   To call sayHi, it must be written as sayHi(); with parentheses.

3. Final Answer:

   Missing parentheses when calling sayHi -> Option D

4. Quick Check:

   Function call needs () [OK]

Hint: Always use () to call a function [OK]

Common Mistakes:

• Omitting parentheses when calling functions
• Confusing function name with variable
• Assuming semicolon alone calls function

5. Given the function below, how would you call multiply to multiply 4 and 5 and print the result?

int multiply(int a, int b) {
    return a * b;
}

int main() {
    // Your code here
    return 0;
}

hard

A. int result = multiply(4, 5);

B. multiply(4, 5);

C. printf("%d", multiply(4, 5));

D. print(multiply(4, 5));

Solution

1. Step 1: Understand multiply function

   It returns the product of two integers.

2. Step 2: Call multiply and print result

   To show output, call multiply(4, 5) inside printf with %d format.

3. Final Answer:

   printf("%d", multiply(4, 5)); -> Option C

4. Quick Check:

   Use printf to display function return [OK]

Hint: Use printf to show returned value from function [OK]

Common Mistakes:

• Calling multiply without printing result
• Using print() instead of printf() in C
• Assigning result but not printing