C经典之9-system,if,do,while---ShinePans

#include <stdio.h>
#include <conio.h>
#include <stdlib.h> //system(); 这个指令需要用到此头文件
#include <ctype.h> //toupper要用到
void main()
{
char letter;
do{
printf("A Display directory listling\n");
printf("B Display disk information\n");
printf("C Change system date\n");
printf("Q Exit\n");
printf("Choice: ");
letter = _getch();
letter = toupper(letter);
if (letter == 'A')
system("DIR");
else if (letter == 'B')
system("CHKDSK");
else if (letter == 'C')
system("DATE");
} while (letter != 'Q');
system("pause");

}