From your experience with Maple you should already be familiar with the concept of a variable. You know that a variable is a named storage location. You know that you can store a value in a variable, and that you can later examine and use that value.
Like Maple, C allows you to use variables. But unlike Maple, in which you can ``make up'' new variables as you go along, with C you have to declare all of the variables that you are going to use in your program.
In other words, before you can use a variable in a C program, you have to tell the compiler something about that variable. Can you think of the things that you would have to declare about a variable?
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This is a very important difference between Maple variables and C variables. In Maple, every variable can hold any kind of data--integers, real numbers, complex numbers, whatever. But in C, each variable is defined to hold exactly one kind of data. For example, a variable named x might be able to hold integers, or it might be able to hold real numbers, but it can't hold both kinds of numbers.