Function calling - Mini Project: Build & Apply

Function calling

📖 Scenario: You are creating a simple program to greet a user by name. The greeting message will be generated by a function.

🎯 Goal: Build a C program that defines a function to print a greeting message and then calls that function from main.

📋 What You'll Learn

Define a function called greet that takes no parameters and returns nothing.

Inside greet, print the message Hello, friend!.

Call the greet function from the main function.

💡 Why This Matters

🌍 Real World

Functions help organize code into reusable blocks, making programs easier to read and maintain.

💼 Career

Understanding function calling is essential for any programming job, as it is a basic building block of software development.

1

Create the greet function

Write a function called greet that takes no parameters and prints Hello, friend! using printf.

C

#include 

// Define the greet function here
// Your code here

int main() {
    return 0;
}

Hint

Use void greet() to define the function and printf to print the message.

2

Call the greet function from main

Inside the main function, call the greet function by writing greet(); before return 0;.

C

#include 

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

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

Hint

Simply write greet(); inside main before return 0;.

3

Add a function prototype for greet

Add a function prototype for greet above main by writing void greet();.

C

#include 

// Add function prototype for greet here
// Your code here

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

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

Hint

Write the prototype void greet(); before the function definitions.

4

Run the program and print the output

Run the program and print the output by writing printf output to the console. The program should print Hello, friend!.

C

#include 

void greet();

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

int main() {
    greet();
    // Output is printed by greet function
    // Your code here
    return 0;
}

Hint

The greet function already prints the message. Just run the program to see the output.

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