How are variables stored in memory, and what determines their addresses?

In C, variables are stored in memory locations, each of which has a unique address. This address is essentially a pointer to where the data is stored in the computer’s RAM. The way variables are stored and their addresses depend on various factors, including the type of variable, the scope of the variable, and the memory allocation method.

1. Memory Management

When a program is compiled, the compiler decides where to store variables based on their types, sizes, and where they are declared. The variables can be stored in different areas of memory:

• Stack: Local variables (those declared inside functions) are typically stored on the stack. The stack is a region of memory that grows and shrinks with function calls and returns. Each time a function is called, space for its local variables is created on the stack, and when the function ends, the space is reclaimed. The stack grows downward, meaning new variables are typically placed at lower memory addresses.
• Heap: Dynamically allocated variables (those created using malloc, calloc, or realloc) are stored in the heap. The heap is a region of memory used for variables whose size or lifetime isn’t known in advance. Memory from the heap must be manually managed (freed using free()).
• Data Segment: Global variables and static variables are stored in the data segment, a part of memory that is initialized when the program starts and persists throughout its lifetime.

2. Address Assignment

The address of a variable is determined by its memory location. For local variables, the compiler assigns addresses based on the current state of the stack. For dynamically allocated memory, the operating system’s memory manager assigns an address from the heap. The address of a variable can be accessed using the address-of operator &, which returns the memory address of that variable.

In summary, the memory address of a variable in C depends on where it is declared (stack, heap, or data segment), its scope, and the way it is allocated, allowing the program to efficiently manage memory.