In the last post I introduced variables in C.

In this post I want to tell you everything about constants in C.

A constant is declared similarly to variables, except it is prepended with the const keyword, and you always need to specify a value.

Like this:

const int age = 37;

This is perfectly valid C, although it is common to declare constants uppercase, like this:

const int AGE = 37;

It’s just a convention, but one that can greatly help you while reading or writing a C program as it improves readability. Uppercase name means constant, lowercase name means variable.

A constant name follows the same rules for variable names: can contain any uppercase or lowercase letter, can contain digits and the underscore character, but it can’t start with a digit. AGE and Age10 are valid variable names, 1AGE is not.

Another way to define constants is by using this syntax:

#define AGE 37

In this case, you don’t need to add a type, and you don’t also need the = equal sign, and you omit the semicolon at the end.

The C compiler will infer the type from the value specified, at compile time.