Adding large number string, conversion, stripping of leading zero string value comparison function template

string S(ll n){stringstream ss;string s;ss<<n;ss>>s;return s;}
ll N(string s){stringstream ss;ll n;ss<<s;ss>>n;return n;}
string rm0(string s){//  去除前导0函数
    int i;
    for(i=0;i<s.size()-1;i++)
        if(s[i]!='0')
            break;
    return s.substr(i);
}
string ADD(string s,string t) {// 字符串整数相加，返回一个字符串
  if(s.size()<t.size())swap(s,t);s='0'+s;
  reverse(t.begin(), t.end());while(s.size()>t.size())t+='0';reverse(t.begin(), t.end());int c=0;
  for(int i=s.size();i>=0;i--)
  {
    if(c){
        if(s[i]=='9'){
            s[i]='0';c=1;
        }else{
            s[i]=(char)(s[i]+1);c=0;
        }
    }
    int sum=(int)s[i]+(int)t[i]-'0'*2;
    if(sum>=10){
        s[i]=(char)(sum-10+'0');c=1;
    }
    else
        s[i]=(char)(sum+'0');
  }
  return rm0(s);
}
bool cmp(string s,string t) {
    // s>=t 返回1
    // s<t 返回0
    if(s.size()!=t.size())
          return s.size()>t.size();
    for(int i=0;i<s.size();i++)
        if(s[i]!=t[i])
            return s[i]>t[i];
  return 1;
}