Static Keyword in C

1#include <stdio.h>
2
3// Function with NORMAL variable
4void normalCounter() {
5    int count = 0;  // Created fresh each call
6    count++;
7    printf("Normal: %d\n", count);
8}
9
10// Function with STATIC variable
11void staticCounter() {
12    static int count = 0;  // Initialized ONCE, persists!
13    count++;
14    printf("Static: %d\n", count);
15}
16
17int main() {
18    printf("=== Normal Variable (resets) ===\n");
19    normalCounter();  // Prints 1
20    normalCounter();  // Prints 1
21    normalCounter();  // Prints 1
22    
23    printf("\n=== Static Variable (persists) ===\n");
24    staticCounter();  // Prints 1
25    staticCounter();  // Prints 2
26    staticCounter();  // Prints 3
27    
28    return 0;
29}

1// file1.c
2static int privateCounter = 0;  // Only visible in file1.c
3int publicCounter = 0;          // Visible everywhere
4
5void incrementPrivate() {
6    privateCounter++;
7}
8
9// file2.c
10extern int publicCounter;       // Can access this ✓
11// extern int privateCounter;   // ERROR! Cannot access static variable ✗

1#include <stdio.h>
2
3// Static function - only visible in this file
4static void helperFunction() {
5    printf("I'm a private helper!\n");
6}
7
8// Normal function - can be called from other files
9void publicFunction() {
10    printf("I'm public!\n");
11    helperFunction();  // Can call static function from same file
12}
13
14int main() {
15    publicFunction();   // Works ✓
16    helperFunction();   // Works (same file) ✓
17    return 0;
18}

1#include <stdio.h>
2
3// Generate unique IDs using static
4int getNextID() {
5    static int id = 1000;  // Starts at 1000, never resets!
6    return id++;           // Return current, then increment
7}
8
9int main() {
10    printf("User 1 ID: %d\n", getNextID());  // 1000
11    printf("User 2 ID: %d\n", getNextID());  // 1001
12    printf("User 3 ID: %d\n", getNextID());  // 1002
13    printf("User 4 ID: %d\n", getNextID());  // 1003
14    
15    return 0;
16}