Introduction to Programming in C

📘 Inline Functions, Static & Extern Keywords in C

This chapter covers three essential components for efficient and modular C programming: inline functions, static variables/functions, and the extern keyword. These help manage scope, linkage, performance, and memory effectively.

🔹 Inline Functions

Inline functions suggest to the compiler to replace function calls with the function’s code directly, reducing function call overhead.

inline int square(int x) {
  return x * x;
}

int main() {
  printf("Square of 5 is %d\n", square(5));
  return 0;
}

• Introduced in C99 (using inline keyword)
• Helps speed up small, frequently called functions
• Compiler may ignore the suggestion

📍 Static Keyword

The static keyword changes the scope and lifetime of variables/functions.

1️⃣ Static Variables Inside Functions

void counter() {
  static int count = 0;
  count++;
  printf("Count = %d\n", count);
}

int main() {
  counter();  // Output: Count = 1
  counter();  // Output: Count = 2
}

Note: Static variables are initialized only once and retain their value between function calls.

2️⃣ Static Global Variables

// file1.c
static int globalCount = 0; // only visible in this file

• Restricts global variable/function access to the same file
• Used to avoid naming conflicts across files

🌐 Extern Keyword

The extern keyword tells the compiler a variable is declared elsewhere. It is used to share global variables/functions between files.

🗂 Multi-file Program Example

📄 file1.c

int globalVal = 100;

📄 file2.c

#include <stdio.h>
extern int globalVal;

int main() {
  printf("Value: %d\n", globalVal);
  return 0;
}

• extern doesn’t allocate memory; it accesses an existing global variable
• Used extensively in multi-file modular projects

📚 UdaanPath Example: Shared Config Values

Suppose you're building a configuration module for UdaanPath:

📄 config.h

extern int maxStudents;
extern char siteName[];

📄 config.c

int maxStudents = 500;
char siteName[] = "UdaanPath";

📄 main.c

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

int main() {
  printf("Platform: %s\n", siteName);
  printf("Max Students: %d\n", maxStudents);
  return 0;
}

📝 Practice Tasks

1. Write an inline function to calculate cube of a number
2. Use static to restrict a global variable
3. Write a multi-file program using extern keyword
4. Create a static counter that retains value between function calls

✅ Summary

• inline: Suggests function expansion to optimize performance
• static: Changes scope, retains value between calls
• extern: Allows accessing global variables/functions across files

🚀 Coming Next

Next, we'll explore Advanced Pointers — including Pointer to Pointer and Function Pointers — to gain deeper control over memory and functions in C.