我的 C++ 变量（与作用域相关）有什么问题？

Question

#include <iostream>
using namespace std;

int main(int argc, char *argv[])
{
    int x = 0, y = 1, k = 5;
{       
    int x = 1;
    x = 10;
    cout << "x is " << x << ", y is " << y << endl;     
}
cout << "x is " << x << " and k is " << k << endl;

cout << endl;
cout << endl;
{
    int x = 5;
    int y = 6;
    {
        int y = 7;
        x = 2;
    }
    cout << "(x, y) is : (" << x << ", " << y << ")" << endl;
}


cin.get();
return 0;
}

The output is:

x is 10, y is 1

x is 0 and k is 5

(x, y) is : (2, 6)

I think (x,y) should be (5,6). Because that's the coordinates x and y are in.

Answer 1

You're modifying x from the outer scope here:

{
    int y = 7; // local variable
    x = 2;     // variable from outer scope
}

If you had said int x = 2; then you could expect to get (5,6) . But you didn't.

Answer 2

您已在最后一个范围内为 x 分配了值 2，因此它是 (2,6)。

Answer 3

Not how it works, because the variable x from the outer scope was the one you changed in the inner scope, where there is no other x to hide it. Consider this example of why this is necessary:

static const size_t N = 10;
size_t i = 0;
int array[N];

while (i < 10) {
  const int x = i*i;
  array[i] = x;
  ++i;
} // We're out of the block where i was incremented.  Should this be an infinite loop?

// Should array be uninitialized because this is the scope it was in and we updated it in a nested scope?