Structure of a C Program

Introduction

• Overview of the lecture on the structure of a C program.
• Previous topics covered: Introduction to C, basics of programming, low-level vs. high-level languages, language translators, features of the C language.

Basic Structure of a C Program

• A C program consists of various sections, some essential and some optional.

1. Documentation Section (Comment Section)

• Purpose: To provide information about the program.
  • Information to include:
    • Author's name
    • Date and time of development
    • Brief description of the program (e.g., "Program for addition of two numbers")
• Comments are ignored by the compiler (two types):
  • Single-line comment: //
  • Multi-line comment: /* comment */
• Importance: Enhances readability and understanding of the program.

2. Link Section

• Purpose: To include header files containing predefined functions.
• Common header files:
  • #include <stdio.h>
    • Provides functions for input/output (e.g., printf, scanf).
  • #include <conio.h>
    • Provides console input/output functions (e.g., getch).
  • #include <math.h>
    • Provides mathematical functions (e.g., sqrt, pow).
  • #include <string.h>
    • Provides string manipulation functions (e.g., strlen, strcmp).

3. Definition Section

• Purpose: To define symbolic constants and macros.
• Example: #define PI 3.14
  • Allows for easy updates and code readability.

4. Global Declaration Section

• Declare variables and functions that can be accessed throughout the program.
• Local variables: Accessible only within the function they are defined.
• Global variables: Accessible from any function in the program.

5. Main Section

• Compulsory: Every C program must have one main function.
• Structure of main:

  int main() {
      // declarations
      // executable statements
      return 0;
  }
  

• Control flow starts at the main function.

6. Sub Program Section

• Contains user-defined functions.
• These can be placed after the main function but are not compulsory.

Example Program

• Basic Program: Print "Hello World"

  #include <stdio.h>
  int main() {
      printf("Hello World");
      return 0;
  }
  

• Addition Program Example:
  • Documentation section included for clarity.
  • Link section and definition using macros.

Conclusion

• Summary of the structure of a C program, highlighting the importance of each section.
• Next topic: Compilation process and converting programs into object code.