Variable Scope (Local vs Global)

Variable scope is a concept in programming that determines where a variable can be accessed from in a program. There are two types of variable scope in C++: local and global.

• Local variables: Local variables are declared within a function or block of code. They can only be accessed from within the function or block of code in which they are declared.
• Global variables: Global variables are declared outside of any function or block of code. They can be accessed from anywhere in the program.

Example of local variable scope:

int main() {
  int local_variable = 10;

  // local_variable can only be accessed from within this function.
  std::cout << local_variable << std::endl;

  // This code will cause an error because local_variable is not accessible here.
  std::cout << global_variable << std::endl;

  return 0;
}

Example of global variable scope:

int global_variable = 20;

int main() {
  // global_variable can be accessed from anywhere in the program.
  std::cout << global_variable << std::endl;

  // This code is also valid.
  int local_variable = global_variable;

  return 0;
}

It is important to be aware of variable scope when writing C++ code. Otherwise, you may accidentally access a variable that is not defined or that you are not supposed to access.

Here are some general rules for variable scope in C++:

• Local variables are scoped to the function or block of code in which they are declared.
• Global variables are scoped to the entire program.
• Variables declared in a function can shadow variables declared in the global scope.
• Variables declared in a block of code can shadow variables declared in the function scope.

By understanding variable scope, you can write more efficient and reliable C++ code.