C supports a variety of variable types (different kinds of
variables for different kinds of data), such as integer for
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
compiler.
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.
