An identifier is a user defined name; both function names and variable names are identifiers. Identifiers must not conflict with keywords such as if and for; for example, you cannot create a function or a variable with the name for.

An if statement is a statement that causes its controlled block to be executed if the logical expression specified in the if statement is true.

An ifstream (pronounced "i f stream") is a stream used for input from a file.

Implementation; see class implementation.

Include; see #include statement.

To increment a variable means to add 1 to its value. This can be done in C++ by using the increment operator, ++.

An index is an expression used to select one of a number of elements of a vector or an array. It is enclosed in square brackets ([ ]). For example, in the expression a[i+1], the index is the expression i+1.

An index variable is a variable used to hold an .

Initialization is the process of setting the initial value of a variable. It is very similar to assignment but is not identical: Initialization is done only once for each variable, when that variable is created, whereas assignment can be done as many times as desired. In particular, you cannot assign a value to a const, but you can, and indeed must, initialize it when it is created.

Input is the process of reading data into the computer from the outside world. A very commonly used source of input for simple programs is the keyboard.

Instruction; see machine instruction.

An int (short for integer) is a type of integer variable that is essentially equivalent to either a short or a long, depending on the compiler you are using. A 16-bit compiler such as Borland C++ 3.1 has 16-bit ints, which are the same size as shorts. A 32-bit compiler such as DJGPP (the compiler on the CD-ROM that comes with this book) has 32-bit ints, which are the same size as longs. Of course, pedants will point out that it is not absolutely guaranteed that an int is the same size as either a short or a long; it's theoretically possible that all three of these variable types are different in size. However, at this writing, all commonly available C++ compilers for microcomputers in fact equate an int with either a short or a long. and it does not appear likely that this situation will change in the near future.

An integer variable is a C++ representation of a whole number. Unlike mathematical integers, C++ integers have a limited range, depending on their types; see the individual types char, short, int, and long for details. The type bool is sometimes also considered an integer variable type.

Interface; see class interface.

I/O is an abbreviation for "input/output". This refers to the process of getting information into and out of the computer; see input and output for more details.

iostream.h is the name of the header file that tells the compiler how to compile code that uses predefined stream variables like cout and operators like <<.

An istream is a stream used for input. For example, cin is a predefined istream that reads characters from the keyboard.

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