the c programming language 2-3

#include<stdio.h>
#define MAXLINELEN 1000
int power(int base,int n)
{
 int i=0;
 int answer=1;
 for(i=0;i<n;i++)
 answer=answer*base;
 return answer;
}
/*strlen函数:返回s的长度*/
int strlen(char *s) 
{
 int i;
 i=0;
 while(s[i]!='\0')
 ++i;
 return i;
}
/*getline函数*/
void getlines(char *s)
{
 int i=0;
 int lim=MAXLINELEN;
 int c;
 for(i=0;i<lim-1&&(c=getchar())!='\n'&&c!=EOF;i++)
 s[i]=c;
}
/*hexalpha_to_int函数：把单个char转换成int*/
int hexalpha_to_int(int c)
{
  if(c>='0'&&c<='9')
  c=c-'0'; 
  else if(c>='a'&&c<='z')
  c=c-'a'+10;
  else if(c>='A'&&c<='Z')
  c=c-'A'+10;
  return c;
}
/**/
int htoi(char s[])
{
 int len;
 int i;
 len=strlen(s);
 int answer=0;
 if(s[0]=='0'&&(s[1]=='X'||s[1]=='x'))
 {
  for(i=2;i<len;i++)
  {
   answer=hexalpha_to_int(s[i])*power(16,len-1-i)+answer;
  }
 }
 else
 {
  for(i=0;i<len;i++)
  {
   answer=hexalpha_to_int(s[i])*power(16,len-1-i)+answer;
   printf("i:%d\n",i);
   printf("hexalpha_to_int(s[i]):%d\n",hexalpha_to_int(s[i]));
   printf("power(16,len-1-i):%d\n",power(16,len-1-i));
   printf("answer:%d\n",answer);
  }
 }
 return answer;
}
main()
{
 char s[MAXLINELEN];
 getlines(s);
 printf("%d\n",htoi(s));
}