Variables

A variable is the name of the memory location. It is used to store information. Its value can be altered and reused several times. It is a way to represent memory location through symbols so that it can be easily identified. Variables are key building elements of the C programming language used to store and modify data in computer programs. A variable is a designated memory region that stores a specified data type value. Each variable has a unique identifier, its name, and a data type describing the type of data it may hold.

Here are some key points about variables:

• A variable must be given a unique name (identifier).
• The data type of a variable determines what kind of data it can hold.
• Variables can be assigned values at the time of declaration or later in the code.

Types of Variables

• Local Variables:
  • Declared inside a function or block.
  • Accessible only within the function or block where they are declared.
  • Not initialized automatically; must be explicitly initialized.
• Global Variables:
  • Declared outside all functions.
  • Accessible throughout the program by all functions.
  • Retain their value throughout the program's execution.
• Static Variables:
  • Retain their value between multiple function calls.
  • Can be local or global.
  • Initialized only once, and their lifetime is throughout the program's execution.
• Automatic Variables:
  • Declared using the auto keyword (though optional as auto is default).
  • Limited to the scope of the block in which they are declared.
• External Variables:
  • Declared using the extern keyword.
  • Allows access to a global variable defined in another file.
• Register Variables:
  • Declared using the register keyword.
  • Suggests storing the variable in the CPU register for faster access (subject to availability).

#include <stdio.h>
int globalVar = 10; // Global variable
int main() {
    int localVar = 5;     // Local variable
    static int staticVar; // Static variable (default value is 0)

    printf("Global Variable: %d\n", globalVar);
    printf("Local Variable: %d\n", localVar);
    printf("Static Variable: %d\n", staticVar);

    return 0;
}