一次做ACM扩展出来的小程序

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
int i, j = 0, length, code[28];
char str[1000];

//对code数组按照要求赋值
//"_" ASCII value is 95
//"." ASCII value is 46
//"a" ASCII valude is 97
code[0] = '_';
code[27] = '.';

for(i = 1; i < 27; i++)
{
code[i] = 'a' + i - 1;
}

printf("PS: \"-1\" means END!!\n");
printf("Please input the num or letter:<0-27 | a-z | \"_\"| \".\" only>\n");

while(scanf("%s", str))
{

length = strlen(str);
if(length == 1)
{
if((str[0] < 'a' || str[0] > 'z') && str[0] != '_' && str[0] != '.' && (str[0] < '0' || str[0] > '9'))
{
printf("Input Error! Input again:\n");
}
else
{
for(i = 0; ; i++)
{
//char型数据处理
if((str[0] - 'a') >= 0)
{
if(code[i] == str[0])
{
printf("The %c is %d\n", str[0], i);
break;
}
}
else if(str[0] == '_' || str[0] == '.')
{
if(str[0] == '_')
{
printf("The _ is %d\n", 0);
break;
}
else if(str[0] == '.')
{
printf("The . is %d\n", 27);
break;
}
}

//int型数据处理
else if(i == atoi(str))
{
printf("The %d is %c\n", i, code[i]);
break;
}
}

}
}
else if(length == 2)
{
//先处理正确的
//
//
//int型的两位数处理
if(((atoi(str) - 10) >= 0) && ((atoi(str) - 27) <= 0) && atoi(str) != -1)
{
for(i = 10; ; i++)
{
if(i == atoi(str))
{
printf("The %d is %c\n", i, code[i]);
break;
}
}
}
else if(atoi(str) == -1)
{
printf("The program ENDED!!\n");
return 0;
}
else
{
printf("Input Error! Input again!\n");
}

}
else
{
printf("Input Error! Input again!\n");
}

}

return 0;
}