C supports a variety of variable types (different kinds of
variables for different kinds of data), such as
integer numbers, and
float for numbers with fractional parts.
You can even define your own types, such as
total for a sum, or
surname for someone's last name. You can also convert a variable
of one type into other types. (This is called type coercion.)
Consequently, the type of a variable is of great importance to the
C requires us to list the names and types of all variables that will be used in a program, and provide information about where they are going to be used. This is called declaring variables. If you fail to declare a variable, or use it as if it were a different type from the type it is declared to be, for example, by assigning a non-integer value to an integer variable, you will receive a compile-time error.