Variables and Data Types

## Learning Objectives - Declare and initialize variables - Understand primitive types - Master type conversion - Learn about constants ## Variables ### Declaration ```c int age; // Declaration age = 25; // Assignment int score = 100; // Declaration + Initialization ``` ### Naming Rules - Start with letter or underscore - Can contain numbers (after first character) - Cannot use reserved words - Case-sensitive ```c int age; // Valid int _count; // Valid int $total; // Valid (but avoid) int 2ndPlace; // Invalid int class; // Invalid (reserved word) ``` ## Primitive Data Types ### Integer Types | Type | Size | Range | |------|------|-------| | `char` | 1 byte | -128 to 127 | | `short` | 2 bytes | -32,768 to 32,767 | | `int` | 2-4 bytes | System-dependent | | `long` | 4-8 bytes | System-dependent | | `long long` | 8 bytes | Very large | ```c char c = 'A'; short s = 32000; int i = 2000000; long l = 9000000000L; long long ll = 9000000000000000000LL; ``` ### Unsigned Types ```c unsigned int u = 100; unsigned char uc = 255; unsigned long ul = 4000000000UL; ``` ### Floating-Point Types | Type | Size | Typical Range | |------|------|---------------| | `float` | 4 bytes | 1.2e-38 to 3.4e38 | | `double` | 8 bytes | 2.2e-308 to 1.8e308 | | `long double` | 16 bytes | Even larger | ```c float pi = 3.14f; double precise = 3.14159265359; long double ld = 3.14159265358979323846L; ``` ### Character Type ```c char grade = 'A'; char newline = '\n'; char ascii = 65; // ASCII value ``` ### Boolean Type (C99) ```c #include bool isActive = true; bool hasPermission = false; ``` ## Type Sizes ```c #include int main(void) { printf("char: %zu bytes\n", sizeof(char)); printf("int: %zu bytes\n", sizeof(int)); printf("float: %zu bytes\n", sizeof(float)); printf("double: %zu bytes\n", sizeof(double)); return 0; } ``` ## Initialization ### Default Values **Warning:** Local variables are not automatically initialized! ```c int x; // Garbage value (undefined) int y = 0; // Explicitly initialized ``` ### Initialization Styles ```c int a = 10; // Direct initialization int b = (int)10; // Cast initialization int c = {10}; // Brace initialization (C99) int d = 0; // Zero initialization ``` ## Type Conversion ### Implicit (Automatic) ```c int i = 100; long l = i; // int to long (automatic) double d = i; // int to double (automatic) char c = 'A'; int x = c; // char to int (automatic) ``` ### Explicit (Cast) ```c double d = 3.99; int i = (int)d; // Truncates to 3 float f = 3.14f; int x = (int)f; // 3 ``` ### Integer Promotion ```c char c1 = 10; char c2 = 20; int sum = c1 + c2; // Promoted to int ``` ## Constants ### const Qualifier ```c const double PI = 3.14159; const int MAX_SIZE = 100; // PI = 3.14; // Error! Cannot modify const ``` ### #define Macro ```c #define PI 3.14159 #define MAX_SIZE 100 #define TRUE 1 #define FALSE 0 ``` ### enum ```c enum Color { RED, GREEN, BLUE }; enum Color myColor = RED; // myColor = 0 enum Day { MON = 1, TUE, WED, THU, FRI, SAT, SUN }; ``` ## Limits ```c #include #include #include int main(void) { printf("INT_MAX: %d\n", INT_MAX); printf("INT_MIN: %d\n", INT_MIN); printf("UINT_MAX: %u\n", UINT_MAX); printf("FLT_MAX: %e\n", FLT_MAX); return 0; } ``` ## Variables Scope ### Block Scope ```c int global = 10; // File scope int main(void) { int local = 20; // Block scope for (int i = 0; i < 5; i++) { // Loop scope // i only exists here } return 0; } ``` ### Global vs Local ```c int counter = 0; // Global void increment(void) { counter++; // Accesses global } int main(void) { int counter = 10; // Local (shadows global) printf("%d\n", counter); // 10 (local) printf("%d\n", ::counter); // Error in C (use different names) return 0; } ``` ## Static Variables ```c void counter(void) { static int count = 0; // Retains value between calls count++; printf("Count: %d\n", count); } int main(void) { counter(); // Count: 1 counter(); // Count: 2 counter(); // Count: 3 return 0; } ``` ## Summary - Variables store data values - Integer types: char, short, int, long, long long - Floating types: float, double, long double - Use `const` or `#define` for constants - Cast for explicit type conversion - Local variables are not auto-initialized - `static` variables retain value between calls - Use `` and `` for type limits