1.  Auto Storage Class:

• The auto storage class is the default for all local variables in C++. If you don’t specify a storage class when declaring a variable, it is assumed to be auto.
• Variables with auto storage class are stored in the stack memory.
  They have a limited scope, typically within the function or block where they are declared.
• These variables have automatic storage duration, meaning they are created when the program enters the block where they are defined and destroyed when the block exits.

void someFunction() {
auto int localVar = 10;
// localVar is an auto variable
}

2. Register Storage Class:

• The register storage class is used to suggest to the compiler that a variable should be stored in a CPU register for faster access.
• Register variables are limited in number and should be used for frequently accessed variables that need to be processed quickly.
• The use of register is just a suggestion to the compiler; it may or may not actually store the variable in a register.

register int count = 0;
// count is a register variable

3. Static Storage Class:

• Variables with the static storage class have a longer lifetime compared to auto variables.
• They retain their values between function calls.
• static variables are initialized only once, at the start of the program execution, and keep their values until the program terminates.
• They are stored in a different part of memory compared to the stack memory, usually in the data segment.

void someFunction() {
static int staticVar = 0;
staticVar++;
// staticVar retains its value between function calls
}

4. Extern Storage Class:

The extern storage class is used when you want to declare a variable that is defined in another file.
It is often used when you have multiple source files in a project, and you want to share a variable among them.
The actual storage for an extern variable is defined in another source file, and you simply declare it in the file where you intend to use it.

// In one.cpp
int globalVar = 42;

// In another.cpp
extern int globalVar; // globalVar is declared, and its storage is defined in another file