比较简单就不说了，只是提醒路过的朋友，注意函数的各种情况及返回条件

#include <cstdio>
int strcmpEx(const char * sa, const char * sb)
{
 const char* stra = sa;
 const char* strb = sb;
 while(*stra!='\0'&&*strb!='\0')
 {
  if (*stra != *strb)
  {
   return *stra - *strb;
  }
  stra++;strb++;
 }
 if (*stra=='\0'&&*strb=='\0')
 {
  return 0;
 }
 else if (*stra=='\0'&&*strb!='\0')
 {
  return (int)*strb * (-1);
 }
 else
 {
  return *stra;
 }
}
int main()
{
 printf("%d\n",strcmpEx("abcdef","abcde"));
}