Valid Number 判断一个数字是否有效

class Solution {
public:
    bool isNumber(const char *s) {
  if(s==NULL)
 return false;
  while(isspace(*s))
 s++;
  if(*s=='+'||*s=='-')
 s++;
  bool eAppear=false;
  bool dotAppear=false;
  bool firstPart=false;
  bool secondPart=false;
  bool spaceAppear=false;


  while(*s!='\0')
  {
  if(*s=='.')
  {
    if(dotAppear||eAppear||spaceAppear)
return false;
else 
dotAppear=true;
  }
  else if(*s=='e'||*s=='E')
  {
  if(eAppear||!firstPart||spaceAppear)
  return false;
  else eAppear=true;
  }
  else if(isdigit(*s))
  {
     if(spaceAppear)
return false;
if(!eAppear)
firstPart=true;
else 
secondPart=true;
  }
  else if(*s=='+'||*s=='-')
  {
  if(spaceAppear)
 return false;
  if(!(*(s-1)=='e'||*(s-1)=='E'))
   return false;
  }
  else if(isspace(*s))
 spaceAppear=true;
  else return false;
  s++;
  }


  if(!firstPart)
 return false;
  else if(eAppear&&!secondPart)
 return false;
  else return true;


}
};