What is typedef and why is it useful?

typedef gives an existing type a new, simpler name — pure syntactic sugar that improves readability and lets you change an underlying type in one place.

typedef unsigned int    uint32;
typedef signed int      int32;
typedef unsigned short  uint16;
typedef signed short    int16;
typedef unsigned char   uint8;
typedef signed char     int8;

// Cleaner than "signed int a, b, c;"
int32 a, b, c;

Why it matters:

1. Readability - uint32 is clearer than unsigned int
2. Portability - Change the underlying type in one place
3. Abstraction - Hide implementation details

Almost all non-basic types use typedef:

// These are actually typedefs, not keywords:
// Unsigned type for sizes (typically unsigned long)
size_t
// Signed version for sizes that can be -1 (error)
ssize_t
// Exactly 32-bit signed integer
int32_t
// Exactly 8-bit unsigned integer
uint8_t

To see how types are defined:

$ echo "#include <stdlib.h>" | gcc -E - | grep "typedef .* ssize_t;"

Common with structs:

typedef struct _node {
    int value;
    struct _node *next;
} node;

// Instead of "struct _node n;"
node n;