Point

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• C++ when compare two char* we can use strcmp(a,b);
  if return 0 it means "a=b";
  if return <0 means "a if return >0 means "a>b";
  we can't compare two *char with ""==", cause it compare the address of the two objects;
• how to printf date like 01:01:02 ?
  use printf("%02d",a);
• sort(a,a+n,cmp);
  cmp(object a,object b){
  //write your own rules;
  }
• when printf keep 2 intrger off the point use%.2f
• radix problem any radix convert10
  ans+=ans*radix+Map[i];
  we use the vector as a dynamic array
  vector a;
  a.push_back((int));
  a.pop_back();