C Syntax and First Program

# CHAPTER 3

C Syntax and First Program #

1. Introduction #

2. Learning Objectives #

• Understand the structure of a C program.

• Explain the purpose of #include and header files.

• Understand the role of the main() function.

• Use printf() to output text.

• Write single and multi-line comments.

3. Anatomy of a C Program #

Let's look at the most famous program in computer science:

#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    return 0;
}

Let's break it down line by line:

4. Semicolons and Curly Braces #

• Semicolons (;): Every executable statement in C must end with a semicolon. Missing a semicolon is the #1 cause of beginner errors.

• Curly Braces ({ }): Used to group multiple statements together into a block (like defining the body of a function).

5. Comments in C #

// This is a single-line comment.

/* 
   This is a 
   multi-line comment.
*/

6. The printf() Function #

#include <stdio.h>

int main() {
    printf("Line 1\n"); // \n moves the cursor to the next line
    printf("Line 2\tTabbed\n"); // \t creates a horizontal tab
    return 0;
}

7. Mini Project: Simple Calculator (Hardcoded) #

#include <stdio.h>

int main() {
    int a = 15;
    int b = 5;

    printf("==== SIMPLE CALCULATOR ====\n");
    printf("Addition: %d\n", a + b);
    printf("Subtraction: %d\n", a - b);
    printf("Multiplication: %d\n", a * b);
    printf("Division: %d\n", a / b);
    printf("===========================\n");

    return 0;
}

*(Note: %d is a format specifier telling printf to insert an integer here. We will cover this deeply in the next chapter).*

8. Memory-Level Explanation #

Execution Flow:
OS -> Calls main() -> Executes printf() -> Returns 0 to OS -> Process terminated.

If you omit return 0;, the C99 standard guarantees it will implicitly return 0, but writing it is best practice.

9. Common Mistakes #

• Forgetting the semicolon: printf("Hi") instead of printf("Hi");.

• Misspelling stdio.h: Using <studio.h> (very common beginner typo).

• Case Sensitivity: Main() or Printf() will cause errors. C is strictly case-sensitive.

10. Best Practices #

• Always indent code inside curly braces for readability.

• Add comments explaining *why* you did something complex.

• Keep the main function at the bottom of the file (or declare functions at the top).

11. Exercises #

1. 1. Write a C program that prints your name, age, and country on three separate lines.

1. 2. Intentionally remove a semicolon from your program and try compiling it. Read the error message.

1. 3. Write a program using multi-line comments at the top containing your name and the date.

12. MCQ Quiz with Answers #

13. Interview Questions #

• Q: Explain the significance of the main() function in C.

• Q: What is a preprocessor directive?

• Q: Why is C case-sensitive, and how does it affect naming?

14. FAQs #

Q: Can I use single quotes for strings? A: No. In C, single quotes ('A') are for single characters, while double quotes ("Text") are for strings.

15. Summary #

16. Next Chapter Recommendation #