求任意底數和任意真數的對數

#include<stdio.h>
#include<math.h>
int loga(int r,int b);
int main(void)
{
  int r,b,l;
  printf("What's the base?\n");
  scanf("%d",&b);
  printf("What's the real number?\n");
  scanf("%d",&r);
  l=loga(r,b);
  printf("The logarithn is %d.\n",l);
  return 0;
}

int loga(int r,int b)
{
  int s=0,i;
  for(i=0;s!=r;i++)
    s=pow(b,i);
  return --i;
}