Structure of a C Program

Introduction

• Discusses the basic structure of a C program.
• Overview of how to write a C program with an example.
• Prior knowledge from videos includes:
  • Introduction to C programming
  • Low-level vs. high-level languages
  • Language translators
  • Features of C language

Basic Structure of a C Program

• Sections of a C program:
  • Some sections are essential, while others are optional.

1. Documentation Section (Comment Section)

• Purpose: To provide information about the program.
• Includes:
  • Author information
  • Date and time of development
  • Brief description of the program
• Comment syntax in C:
  • Single line: // comment
  • Multi-line: /* comment */
• Importance:
  • Helps future users understand the program.

2. Link Section

• Includes header files using #include directive.
• Example: #include <stdio.h> for standard input/output functions.
• Purpose:
  • Predefined functions (e.g., printf, scanf) are defined in header files.
  • Compiler needs these definitions to understand function calls.
• Other header files examples:
  • #include <math.h> for mathematical functions.
  • #include <string.h> for string functions.

3. Definition Section

• Defines symbolic constants using #define.
• Example:
  • #define PI 3.14
• Benefits:
  • Easier to manage constants.
  • Facilitates updates (change in one place reflects everywhere).

4. Global Declaration Section

• Declaration of global variables and functions.
• Global variables can be accessed throughout the program.
• Example:
  • int a; declared outside any function can be used in all functions.

5. Main Function

• Mandatory Section: Every C program must include a main function.
• Syntax:
  • void main() { }
• Structure:
  • Declaration part: Variable declarations.
  • Executable part: Logic of the program.
• Control always starts from the main function when the program is executed.

6. Subprogram Section

• Contains user-defined functions.
• Typically placed after the main function.

Example Program

• A simple program to illustrate the structure:

  #include <stdio.h>
  
  void main() {
      printf("Hello World\n");
      getch();
  }
  

• Further example with additional sections and functions explained:

  // Documentation section
  #include <stdio.h>
  
  #define MAX 100
  
  void display();  // Function declaration
  
  int main() {
      int a = 50;  // Declaration part
      printf("Hello\n");  // Executable part
      display();  // Calling user-defined function
      getch();
  }
  
  void display() {  // Function definition
      printf("Jenny's Lectures\n");
  }
  

• Execution flow:
  1. Control goes to main, prints "Hello".
  2. Calls display, prints "Jenny's Lectures".
  3. Returns control to main.

Conclusion

• The structure of a C program involves various sections, each serving a distinct purpose.
• In the next video, the compilation process will be discussed, detailing how the program is converted into object code and executable code.