C Data Types

C provides rich basic types and derived types. This chapter will systematically organize integers, floating-point types, character types, enumerations, arrays, structures, unions, pointers, etc.

1. Basic Types

• Integer types: short, int, long, long long (signed/unsigned)
• Character types: char (often used to store characters or small integers)
• Floating-point types: float, double, long double
• Boolean: _Bool or bool in stdbool.h

Example:

#include <stdbool.h>
short s = 1; unsigned int ui = 10u; long long ll = 1000ll;
char c = 'A'; bool ok = true; double pi = 3.14159;

2. Literals and Suffixes

• Integer suffixes: u, l, ll
• Floating-point suffixes: f, l
• Number bases: hexadecimal 0x2A, octal 052, binary (not standardized before C23, can use macros/libraries)

3. sizeof and Alignment

printf("%zu\n", sizeof(int));

sizeof returns the number of bytes occupied by an object or type.

4. Type Conversion

• Implicit conversion: small types are promoted to larger types during arithmetic operations
• Explicit conversion: (int)3.14

5. Enumerations (enum)

enum Color { RED=1, GREEN=2, BLUE=3 };

6. Derived Types Overview

• Arrays: int a[10];
• Pointers: int *p;
• Structures: struct Point { int x; int y; };
• Unions: union Data { int i; float f; char c; };

7. Constant Qualifiers and Qualifiers

• const read-only
• volatile prevents optimization from ignoring changes (e.g., hardware registers)
• restrict pointer aliasing optimization hint (C99)

8. Characters and Strings

• Character constants: 'A'