Writing Your First C Program – Syntax and Structure
Now that you have an understanding of what C is and why it is important, it’s time to write and run your first C program. In this chapter, we will cover the basic syntax and structure of a C program, understand how it works, and explore essential concepts such as header files, main function, statements, and comments.
Writing Your First C Program
Before we dive into the details, let’s look at a simple C program that prints “Hello, World!” on the screen. This is traditionally the first program written in any language.
Example: “Hello, World!” in C
#include <stdio.h> // Header file for standard input-output functions
int main() { // Main function – entry point of a C program
printf(“Hello, World!\n”); // Prints text to the console
return 0; // Indicates that the program executed successfully
}
📌 Output:
Hello, World!
Understanding the Structure of a C Program
Every C program follows a specific structure. Let’s break it down:
Basic Structure of a C Program
#include <header_file> // Preprocessor directive
int main() { // Main function
// Statements inside the function
return 0; // Return statement
}
Key Components of a C Program
| Component | Description |
| Preprocessor Directives | Used to include header files. Example: #include <stdio.h> |
| Main Function (main()) | Every C program must have a main() function as the starting point. |
| Statements & Expressions | Code inside {} that performs operations. Example: printf(“Hello, World!”); |
| Return Statement (return 0;) | Indicates successful execution of the program. |
Header Files and Preprocessor Directives
In C, we use header files to access built-in functions. The #include directive tells the compiler to include the contents of a file before compilation.
Common Header Files in C
| Header File | Purpose |
| <stdio.h> | Standard Input/Output functions (e.g., printf, scanf) |
| <stdlib.h> | General utilities (e.g., malloc, free, exit) |
| <math.h> | Math functions (e.g., sqrt, pow) |
| <string.h> | String handling (e.g., strlen, strcpy) |
Example:
#include <stdio.h> // Includes standard input-output functions
The main() Function
The main() function is where program execution begins. Every C program must have a main() function.
Example:
int main() {
printf(“Welcome to C Programming!\n”);
return 0;
}
🔹 int before main indicates that the function returns an integer (0 means successful execution).
Printing Output in C (printf)
To display text on the screen, we use the printf() function from <stdio.h>.
Example: Using printf()
#include <stdio.h>
int main() {
printf(“C programming is fun!\n”);
printf(“I am learning C.\n”);
return 0;
}
📌 Output:
C programming is fun!
I am learning C. 🔹 \n (newline character) moves text to the next line