八进制转换为十进制

#include<stdio.h>
#include<stdlib.h>
int main()
{
   int n=0,i=0;
   char s[20];
   printf("please input a Octal :\n");
   gets(s);
   while(s[i]!='\0'){
   n=n*8+s[i]-'0';
   i++;
  }
  printf("changed to decimal\n%d\n",n);
  return 0;
}