Scope of Loop Variables

In C++, variables declared within the initialization statement of a for loop have a scope limited to the loop body. The variables are only accessible within the loop and are destroyed at the end of each iteration. Example:

1#include <iostream>
2
3int main() {
4  for (int i = 0; i < 5; ++i) {
5    // i is accessible within the loop body
6    std::cout << i << "\n";
7  }
8  // i is not accessible outside the loop
9  std::cout << i << "\n"; 
10}

1error: 'i': undeclared identifier

In this example, the variable i is declared within the initialization statement of the for loop. It is accessible only within the loop body and cannot be used outside the loop.

If you need to access the loop variable after the loop ends, you can declare it before the loop and use it within the loop initialization statement:

1#include <iostream>
2
3int main() {
4  int i;
5  for (i = 0; i < 5; ++i) {
6    // i is accessible within the loop body
7    std::cout << i << "\n";
8  }
9  // i is accessible here
10  std::cout << "Final value of i: " << i << "\n";
11}

10
21
32
43
54
6Final value of i: 5

By declaring the variable i outside the loop, you can control its scope and access it after the loop if needed.

The scope rules for variables declared in the initialization statement of a for loop apply to all versions of C++, ensuring consistent behavior across different standards.