Defining structures

A structure in C provides a way to use custom data types beyond the basic ones provided. This can often simplify problems in the way they are handled.

As an example, let us imagine we are designing a program to handle fractions, which are defined by an integer numerator and denominator. One could introduce two int variables to represent the numerator and denominator; alternatively, one can introduce a structure with two int members:

struct frac {
  int n, d;
};

Subsequently, in a program

  struct frac f1;
  f1.n = 1;
  f1.d = 3;
  printf("The fraction is %d / %d\n", f1.n, f1.d);

one can refer to the basic fraction entity by a single name (f1, in this case), and access individual members of the structure by the dot notation - f1.n for the numerator, and f1.d for the denominator.

Some prefer to define structures through the use of a typedef declaration:

typedef struct {
  int n, d;
} frac;

so that variables can be defined without having to specify the struct keyword:

  frac f1;
  f1.n = 1;
  f1.d = 3;
  printf("The fraction is %d / %d\n", f1.n, f1.d);