怎么用程序判断输入是否正确呢,并且在错误时候输出error
#include <stdio.h>
int main()
{
char ch;
printf("请输入第一个字母:");
scanf("%c", &ch);
if (ch=='m') printf("monday\n");
if (ch=='t')
{
getchar();
printf("请输入第二个字母:");
scanf("%c", &ch);
if(ch=='u')printf("tuesday\n");
else if(ch=='h')printf("thursday\n");
else
printf("error");
} if (ch == 'w')printf("wednesday\n");
if (ch == 'f')printf("friday\n");
if (ch == 's')
{
getchar();
printf("请输入第二个字母:");
scanf("%c", &ch);
if (ch == 'a')printf("saturday\n");
else if printf("sunday\n");
else printf("error");
}
else
printf("error");
}