#include <iostream>
using namespace std;
int main()
{
char c1[BUFSIZ] = { 0 }, c2[BUFSIZ] = {0};
cout << "请输入字母:" << endl;
cin >> c1;
int i = 0;
int num = strlen(c1);
while (c1[i] != '\0')
{
for (i = 0; i < num; i++)
{
if (c1[i] >= 'A' && c1[i] <= 'Z')
{
c2[i] = c1[i] + 32;//大写转小写
}
if (c1[i] >= 'a' && c1[i] <= 'z')
{
c2[i] = c1[i] - 32;//小写转大写
}
}
cout << c2 << endl;
}
}
