Variables are named memory locations that hold data which can change during program execution. Constants are fixed values that cannot be altered. You can declare a constant using the const keyword or #define preprocessor.

Variables must be declared before use, and a meaningful name should be assigned. Constants are useful for defining fixed values like PI or limits. Initialization at declaration is good practice. Variable names must begin with a letter or underscore. Proper naming enhances code readability and debugging.

Examples:

const float PI = 3.14;
#define MAX 100
int number = 10;