In C++, there are several types of variables, each of which can store a different kind of data. The main types of variables are:

1. Primitive data types: These are the basic building blocks of C++ and include integer, floating-point, character, boolean, and void data types.

2. Array variables: An array is a collection of elements of the same data type that are stored in contiguous memory locations.

3. Pointer variables: A pointer is a variable that stores the memory address of another variable.

4. Reference variables: A reference is an alias for another variable. It provides an alternative name for an existing variable and allows you to access and modify the original variable using the reference.

5. User-defined data types: These are data types that you define yourself using classes, structures, and unions.

Here is a brief overview of each type of variable:

1. Primitive data types:

• int: used to store whole numbers
• float and double: used to store decimal numbers with varying levels of precision
• char: used to store single characters
• bool: used to store true or false values
• void: used to represent the absence of a type, typically used for functions that do not return a value.

2. Array variables:

• Arrays are used to store a collection of elements of the same data type, with each element identified by an index.

3. Pointer variables:

• Pointers are used to store the memory address of another variable. They are useful for dynamic memory allocation and passing data between functions.

4. Reference variables:

• References provide an alternative name for an existing variable. They are useful for passing data between functions and for providing a shorthand way to access complex data structures.

5. User-defined data types:

• Classes: used to define complex data types that include both data and functions
• Structures: used to group related data elements together
• Unions: used to store different data types in the same memory location.