Writing first C program - Mini Project: Build & Apply

Writing first C program

📖 Scenario: You want to create a simple C program that prints a friendly greeting message on the screen. This is like writing a short note to say hello to your computer.

🎯 Goal: Build a C program that prints the message Hello, World! to the console.

📋 What You'll Learn

Create a main function

Include the stdio.h header

Use printf to display the message

Return 0 from main

💡 Why This Matters

🌍 Real World

Printing messages is the first step in learning how to communicate with a computer using code.

💼 Career

Understanding basic program structure and output is essential for all software development jobs.

1

Include the standard input-output header

Write the line #include <stdio.h> at the top of your program to include the standard input-output library.

C

# Your code here

Hint

This line tells the computer to include the code needed to print messages on the screen.

2

Create the main function

Write the line int main() followed by an opening curly brace { to start the main function.

C

#include 

# Your code here

Hint

The main function is where your program starts running.

3

Print the greeting message

Inside the main function, write the line printf("Hello, World!\n"); to print the greeting message.

C

#include 

int main() {
    # Your code here
}

Hint

The \n adds a new line after the message.

4

Close the main function and return 0

Add the line return 0; and then a closing curly brace } to end the main function.

C

#include 

int main() {
    printf("Hello, World!\n");
    # Your code here
}

Hint

Returning 0 means the program finished successfully.

Practice

1. What is the purpose of the int main() function in a C program?

easy

A. It prints messages to the screen.

B. It is the starting point where the program begins execution.

C. It declares variables for the program.

D. It ends the program immediately.

Solution

1. Step 1: Understand the role of main()

   The main() function is where the program starts running in C.

2. Step 2: Identify the correct purpose

   It is not for declaring variables or printing messages but for starting the program.

3. Final Answer:

   It is the starting point where the program begins execution. -> Option B

4. Quick Check:

   Program starts at main() [OK]

Hint: Remember: C programs always start at main() [OK]

Common Mistakes:

• Thinking main() prints output
• Confusing main() with variable declaration
• Believing main() ends the program immediately

2. Which of the following is the correct syntax to print "Hello, World!" in C?

easy

A. printf("Hello, World!");

B. printf("Hello, World!")

C. print("Hello, World!");

D. echo("Hello, World!");

Solution

1. Step 1: Identify the correct function for output

   In C, printf is used to print text to the screen.

2. Step 2: Check syntax details

   Each statement must end with a semicolon ;. So printf("Hello, World!"); is correct.

3. Final Answer:

   printf("Hello, World!"); -> Option A

4. Quick Check:

   Use printf with semicolon [OK]

Hint: Always end printf with a semicolon [OK]

Common Mistakes:

• Missing semicolon at the end
• Using print instead of printf
• Using echo which is not C syntax

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

#include 
int main() {
    printf("Welcome to C programming!\n");
    return 0;
}

medium

A. No output

B. Welcome to C programming!\n

C. Syntax Error

D. Welcome to C programming!

Solution

1. Step 1: Understand the printf statement

   The string inside printf includes \n which means new line after printing.

2. Step 2: Predict the output

   The program prints "Welcome to C programming!" followed by a new line.

3. Final Answer:

   Welcome to C programming! -> Option D

4. Quick Check:

   \n creates new line, output is plain text [OK]

Hint: \n means new line, not literal text [OK]

Common Mistakes:

• Thinking \n prints as text
• Expecting syntax error due to \n
• Ignoring the return statement effect

4. Identify the error in the following C program:

#include 
int main() {
    printf("Hello World")
    return 0;
}

medium

A. Incorrect header file included

B. Missing return type for main

C. Missing semicolon after printf statement

D. Missing main function

Solution

1. Step 1: Check each statement for syntax

   The printf statement is missing a semicolon at the end.

2. Step 2: Verify other parts

   The main function has correct return type and header file is correct.

3. Final Answer:

   Missing semicolon after printf statement -> Option C

4. Quick Check:

   Every statement ends with ; [OK]

Hint: Look for missing semicolons after statements [OK]

Common Mistakes:

• Ignoring missing semicolon errors
• Thinking return type is missing
• Assuming wrong header file causes error

5. You want to write a C program that prints two lines: "Hello!" and "Welcome to C." Which code snippet correctly does this?

hard

A. #include
int main() {
printf("Hello!\n");
printf("Welcome to C.\n");
return 0;
}

B. #include
int main() {
printf("Hello!Welcome to C.\n");
return 0;
}

C. #include
int main() {
printf("Hello!");
printf("Welcome to C.\n");
return 0;
}

D. #include
int main() {
printf("Hello!");
printf("Welcome to C.");
return 0;
}

Solution

1. Step 1: Understand how to print two lines

   Each line should end with a newline character \n to move to the next line.

2. Step 2: Check each option for correct newlines

   #include int main() { printf("Hello!\n"); printf("Welcome to C.\n"); return 0; } prints "Hello!" with \n and "Welcome to C." with \n, so two lines appear.

3. Final Answer:

   Two printf statements, each ending with \n -> Option A

4. Quick Check:

   Use \n at end of each line for separate lines [OK]

Hint: Use \n after each line to print on new lines [OK]

Common Mistakes:

• Missing \n causing lines to join
• Putting \n only on first line
• Not returning 0 at end of main