十进制转换为其他进制数

#include<stdio.h>

char change(int r)
{
if(r<10)
return(r+'0');
if(r == 10)
return'A';
if(r == 11)
return'B';
if(r == 12)
return'C';
if(r == 13)
return'D';
if(r == 14)
return'E';
if(r == 15)
return'F';
}

int main()
{
int R,m,i,n,r,j;
char sum[100];
while(scanf("%d%d",&m,&R) != EOF)
{
i = 0;
if(m<0)
{
n = -m;
printf("-");
}
else
n = m;
if(n <= R )
printf("%d",change(n));
while(n != 0)
{
r = n % R;
n = n / R;
sum[i] = change(r);
i++;
}
for(j=i-1; j>=0; j--)
printf("%c",sum[j]);
printf("\n");
}
}