十进制转换任意进制

#include <stdio.h>
#include <stdlib.h>
char* itoa(int num,char*str,int radix)
{
char *index = "0123456789ABCDEFGHIJKLMNOPQUVWXYZ";
char t;
int i = 0,unum,k,j;
if(radix == 10 && num < 0){
unum = -num;
str[i++] = '-';
}else{
unum = num;
}
do{
str[i++] = index[unum % radix];
unum /= radix;
}while(unum);
str[i] = '\0';
k = str[0] == '-' ? 1 : 0;

for(j = k; j <= (i - 1)/2; j++)
{
t = str[j];
str[j] = str[ i - 1 + k - j];
str[i - 1 + k - j] = t;
}
return str;
}
int main()
{
int a = 3;
char two[30];
itoa(a,two,2);
printf("%s\n",two);
}