源代码：
#include<stdio.h>
#include<stdlib.h>
typedef long long LL;
const LL N=100000;
char judge(LL );
int main(){
LL a,i,ge,k=0;
char b[N];
scanf("%lld",&a);
while(1){
ge = a%16;
b[k++]=judge(ge);
a = a/16;
if(a==0) {
k--;
break;
} //此处防止多输出一个0；此处容易出错
if(a<16){
b[k]=judge(a);
break;
} //a<16,就不需要再向前判断了。
}
for(i=k;i>=0;i--)
printf("%c",b[i]);
return 0;
}
char judge(LL n){
switch(n){
case 0:return '0';
case 1:return '1';
case 2:return '2';
case 3:return '3';
case 4:return '4';
case 5:return '5';
case 6:return '6';
case 7:return '7';
case 8:return '8';
case 9:return '9';
case 10:return 'A';
case 11:return 'B';
case 12:return 'C';
case 13:return 'D';
case 14:return 'E';
case 15:return 'F';
}
}