Introduction to Programming in C

📘 Header Files and Modular Programming in C

As your programs grow larger, organizing your code becomes essential. C supports modular programming using header files and separate source files to improve readability, maintainability, and reusability.

🔹 What are Header Files?

Header files (with .h extension) contain declarations of functions, macros, constants, and types. They allow you to share declarations across multiple C files.

📁 Standard Header Files

• stdio.h — Standard input/output functions
• stdlib.h — General utility functions
• string.h — String manipulation functions
• math.h — Mathematical functions
• ctype.h — Character handling functions

🛠 How to Create a Custom Header

📄 mathutils.h

// mathutils.h
#ifndef MATHUTILS_H
#define MATHUTILS_H

int add(int a, int b);
int subtract(int a, int b);

#endif

🧠 mathutils.c

// mathutils.c
#include "mathutils.h"

int add(int a, int b) {
  return a + b;
}

int subtract(int a, int b) {
  return a - b;
}

💻 main.c

#include <stdio.h>
#include "mathutils.h"

int main() {
  printf("Add: %d\n", add(5, 3));
  printf("Subtract: %d\n", subtract(10, 4));
  return 0;
}

📚 UdaanPath Example: Utilities Module

Suppose you're building a student management app on UdaanPath. You can organize your code into:

• student.h — function declarations for student operations
• student.c — function definitions (e.g., addStudent, removeStudent)
• main.c — your main logic that uses student module

🎯 Advantages of Modular Programming

• Reduces complexity by splitting code into logical parts
• Makes debugging and testing easier
• Enables code reuse across projects
• Helps with team collaboration in large projects

⚠️ Tips and Best Practices

• Always use #ifndef / #define to prevent multiple inclusions
• Use meaningful file and function names
• Keep declarations in headers, definitions in .c files
• Use comments to explain file/module purposes

📝 Practice Tasks

1. Create a calculator.h and calculator.c to perform arithmetic operations
2. Organize student data management into header and source files
3. Write a reusable module to log user activity

✅ Summary

• Header files allow sharing of function declarations across files
• Modular programming improves code structure, readability, and collaboration
• Use guards (#ifndef) to avoid multiple inclusions

🚀 Coming Next

Next, we’ll cover Preprocessor Directives and Macros — powerful tools that run before compilation and control how your code is built.