What are the basic rules for defining variables in C++?

To declare a variable, you need to know what data type it is going to be of and what its name would be. The variable name has constraints on what you can name it. Following are the rules for naming variables −

• Variable names in C++ can range from 1 to 255 characters.
• All variable names must begin with a letter of the alphabet or an underscore(_).
• After the first initial letter, variable names can also contain letters and numbers.  
• Variable names are case sensitive.
• No spaces or special characters are allowed.
• You cannot use a C++ keyword (reserved word) as a variable name.

Here are some examples of acceptable variable names −

mohd       Piyush    abc   move_name   a_123
myname50   _temp      j     a23b9      retVal

Syntax

You can declare variables using the syntax −

datatype variable_name;

For example,

int my_var;
float my_float;
...