为什么我的 if/else 语句没有产生预期的结果？

我的程序有问题。我实际上已经完成了它，但最后并没有正常工作。我用两种方式编写了它，一种是使用 switch 语句，另一种是使用 if else 语句，但两者都无法正常工作。它们都为我编译并具有干净的构建，但不会按预期运行。

#include <iostream> 
#include <cstdio>
#include <iomanip>
using std::cout;
using std::cin;
using std::endl;
int main()
{
    int i = 0;
    const int size = 27;
    char newline = 'n';
    char *pnumber = 0;
    int selection = 0;
    cout << "PRINGING CONTENTS OF ARRAY" << endl;
    cout << "====================================================" << endl;
    char alphabet[size] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J'
    , 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y'
    , 'Z' , 0 };
     for (i = 0; i < size; i++)
     {
         cout << alphabet[i] << " ";
     }
     cout << newline;
     cout << newline;
     cout << "This is the title to your Program related to the alphabet."
     << endl;
     cout << endl;
     cout << "Select the index that coincides with the alphabet." << endl;
     cout << "For example, the number 7 should display the letter G" << endl;
     cout << endl;
     cout << "Enter an index between 1 and 26: ";
     cin >> i;
     cout << "The number you selected: " << i;
     cout << newline;
     cout << "The letter at this index: " << alphabet[i - 1];
     cout << endl;
     cout << newline;
     cout << newline;
     cout << "PRINTING CONTENTS OF ARRAY and adding x to every other element" << endl;
     pnumber = &alphabet[1];
     for (i = 0; i < size; i += 1)
     {
         if (i % 2 == 0)
         {
             cout << alphabet[i] << " ";
         }
    else
         {
             cout << "x ";
         }
     }
     cout << newline;
     cout << newline;
     cout << "PRINTING CONTENTS OF ARRAY USING THE MOD Option" << endl;
     cout << "=========================================================" << endl;
     cout << "Do you want the letters of the alphabet starting from index 0, A, or index 1, B: ";
     cin >> selection;
      switch (selection)
     {
         case 0:
         {
             for (i = 0; i < size; i += 2)
             {
                 cout << "Even Numbered Elements=" << i << " ";
                 cout << "Contents of Element within Array is=" << alphabet[i];
                 break;
             }
         }
         case 1:
         {
             for (i = 1; i < size; i += 2)
             {
                 cout << "Odd Numbered Elements=" << i << " ";
                 cout << "Contents of Element within Array is=" << alphabet[i] << endl;
                 break;
         }
     }
     default: cout << "You entered an invalid esponse.";
     }
     cout << endl;
     return 0;
 } //End of Int Main

如果其他的话，最后一部分是这样的：

cout << newline;
cout << newline;
cout << "PRINTING CONTENTS OF ARRAY USING THE MOD Option" << endl;
cout << "=========================================================" << endl;
cout << "Do you want the letters of the alphabet starting from index 0, A, or index 1, B: ";
cin >> selection;
if (selection = 0){
    for (i = 0; i < size; i += 2)
    {
        cout << "Even Numbered Elements=" << i << " ";
        cout << "Contents of Element within Array is=" << alphabet[i] << endl;
    }
}
else{
    for (i = 1; i < size; i += 2)
    {
        cout << "Odd Numbered Elements=" << i << " ";
        cout << "Contents of Element within Array is=" << alphabet[i] << endl;
    }
}
return 0;
} //End of Int Main

1(第一部分输出字母表，2(接下来它提示输入一个数字并给出相关的字母，3(接下来程序应该输出，其他每个字母都是x，例如A x C x E x.......。4(最后，它应该提示用户选择O以从A或1开始字母表并启动B，然后它将每隔一个字母输出一次。最后一部分不起作用。它不提供选项，而是每次都做同样的事情。我已经以其他方式对其进行了调整，它两次都会做一个或另一个，而不是一个或另一个。我做错了什么？