Difference between revisions of "Variables, expressions, and operators"
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==Declaration== | ==Declaration== | ||
− | A variable can be declared as <code>datatype identifier</code> | + | A variable can be declared as <code>datatype identifier;</code> |
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+ | Multiple variables can be declared in one line, for example <code>int x, y, z;</code> | ||
==Initialization== | ==Initialization== |
Revision as of 23:59, 20 January 2018
Variables in C++ are used for storing values which are usually input, manipulated, and output. Variables must be explicitly declared as a specific data type (e.g. basic data types) before usage.
Contents
Identifiers
As in regular mathematics, variables have a name that we call an identifier in C++. Identifiers have various rules and conventions.
Identifier rules
Identifiers must adhere to the following rules:
- May only contain alphabetic characters, digits, and underscores
- May not contain any special characters or spaces
- May not start with a digit
- May not be a reserved word
- May not be identical to other identifiers in the same scope
Identifier conventions
Although the following are all legal, identifiers should typically:
- Not start with an underscore (these are frequently used for header files)
- Not be all capital letters, unless used as a constant
- Be descriptive about what is to be stored in them to help with code readability
Identifiers may, additionally, adhere to one of many established naming conventions.
Declaration
A variable can be declared as datatype identifier;
Multiple variables can be declared in one line, for example int x, y, z;
Initialization
Variables can be initialized upon declaration or later. Variables should always have some value placed in them (via input from the user and/or a file or via initialization) before they are used in any calculations or output, otherwise erroneous results may occur.
int age = 30; // Initialization upon declaration
double rate;
rate = 0.05; // Initialization later
Assignment
Variables can be assigned values as such: x = expression;