Sometimes it is convenient to give a new name to a type. You can do this using the typedef statement. Here is the general form of the typedef statement:

typedef old-type-name new-type-name

old-type-name is the existing name for the type, and may consist of more than one token (e.g., unsigned long int). new-type-name is the resulting new name for the type, and must be a single identifier. Creating this new name for the type does not cause the old name to cease to exist. Here are some examples:

typedef unsigned char byte_type;
typedef double real_number_type;

In the case of custom data types, you can use typedef to make a new name for the type while defining the type:

typedef struct fish {
    float weight;
    float length;
    float probability_of_being_caught;
} fish_type;

To make a type defintion of an array, you first provide the type of the element, and then establish the number of elements at the end of the type definition:

typedef char array_of_bytes [5];
array_of_bytes five_bytes = {0, 1, 2, 3, 4};

When selecting names for types, you should avoid ending your type names with a _t suffix. The compiler will allow you to do this, but the POSIX standard reserves use of the _t suffix for standard library types names.