AC code:
#include<stdio.h>
#include<string.h>
int main(){
int n,i,len,sum;
char s[50];
scanf("%d",&n);
getchar(); //缓存回车键
while(n--){
sum = 0;
gets(s); //gets接受回车键
len=strlen(s);
if(s[0] >= '0' && s[0] <= '9') printf("no\n");
else{
for(i = 0; i < len; i++){
if((s[i] >= '0' && s[i] <= '9')||(s[i] >= 'a' &&
s[i] <= 'z')||(s[i] >= 'A' && s[i] <= 'Z')||s[i] == '_')
sum++;
}
if(sum == len) printf("yes\n");
else printf("no\n");
}
}
return 0;
}