Learning C++ – 4 Posts

• 10/16/2024 13:00

  moose 00

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  Hi,
  
  I thought it's time to me to learn C++. To train, I've took a look at TopCoder and just found this exercise ( SRM 100 - Motorola Single Round Match 100 Round 1 - Division II, Level One, Link):
  

  Problem Statement
      	A letter-string is composed of letters ('A'-'Z','a'-'z') and dashes ('-'). The length of a letter-string is the number of characters in it not including dashes (in other words, the number of letters in the string). Given a list of letter-strings you will return the sum of their lengths. 
  
  
  
  Create a class LetterStrings that contains the method sum, which takes a String[], s, and returns an int representing the sum of the lengths of the given letter-strings.
   
  Definition
      	
  Class:	LetterStrings
  Method:	sum
  Parameters:	String[]
  Returns:	int
  Method signature:	int sum(String[] s)
  (be sure your method is public)
      
   
  Constraints
  -	s will contain between 1 and 50 elements, inclusive.
  -	Each element of s will have length between 1 and 50, inclusive.
  -	Each element of s will contain only letters ('A'-'Z','a'-'z') and dashes ('-').
   
  Examples
  0)	
      	
  {\"-\"}
  Returns: 0
  1)	
      	
  {\"A\"}
  Returns: 1
  2)	
      	
  {\"-----Abc\"}
  Returns: 3
  3)	
      	
  {\"-A-B-C-D\", \"--------EFGHI\", \"JKLMNOPQR\", \"---STU-VW-XYZ\"}
  Returns: 26

  
  
  Now I've created this piece of code:
  

  #include <iostream>
  #include <string>
  
  using namespace std;
  
  class LetterStrings {
      public:
          int sum(string s[]);
  };
  
  int LetterStrings::sum(string s[])
  {
      int summe = 0;
      for(int el=0; s[el] != \"0\"; el++){
          for(int i=0; i < s[el].length(); i++){
              if( isalpha(s[el][i]) ) {
                  summe += 1;
              }
          }
      }
    return summe;
  }
  
  int main()
  {
      LetterStrings a, b;
      string str[5] = {\"-A-B-C-D\", \"--------EFGHI\", \"JKLMNOPQR\", \"---STU-VW-XYZ\"};
      cout << a.sum(str) << endl;
  }

  
  
  It seems to work, but I'm not quite sure if it fits the requirements (Method signature: int sum(String[] s)?)
  
  What could be done better in this code?
  
  edit: Just found the statistics with the top-solution:
  

  #include <string>
  #include <vector>
  #include <sstream>
  #include <algorithm>
  #include <iterator>
  #include <iostream>
  #include <cmath>
  #include <cctype>
  #include <cstdio>
  #include <utility>
  using namespace std;
   
  ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
  #define VI vector<int>
  #define VVI vector<vector<int> >
  #define VS vector<string>
  #define si size()
  #define len length()
  ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
   
  class LetterStrings
  {
    public:
    int sum(vector <string> s)
    {
      int ret=0;
      for(int c=0;c<s.si;c++)
        for(int d=0;d<s[c].len;d++)
          if(isalpha(s[c][d]))
            ret++;
      return ret;
    }
  };
   
  // Powered by PopsEdit

  
  isalpha is obviously better then my check via ASCII-Table codes (I've edited my solution), but the top-solutions seems to include quite a lot which isn't needed.

  Edited by moose 09/08/2011 09:01 ago

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• 10/16/2024 13:00

  dloser 00

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  Hi moose,
  
  

  Quote from moose:

  I thought it's time to me to learn C++.
  

  
  Oh boy...
  
  

  Quote:

  
  It seems to work, but I'm not quite sure if it fits the requirements (Method signature: int sum(String[] s)?)
  

  
  I suspect the exercise was made with Java in mind. For C++ using vector is probably closest to String[], both being classes with similar methods.
  
  

  Quote:

  
  What could be done better in this code?
  

  
  

  Quote:

  
  

  class LetterStrings {
      public:
          int sum(string s[]);
  };
  

  
  

  
  The whole class thing is probably just because of Java, but in any case making the method sum static would be appropriate here, I think.
  
  

  Quote:

  
  

      int summe = 0;
  

  
  

  
  Not sticking with English... (Sorry.)
  
  

  Quote:

  
  

      for(int el=0; s[el] != \"0\"; el++){
  

  
  

  
  Just using \"\" here would work as well. Nevertheless it shows that the whole string[] business makes things ugly. For example, an empty string in the input cuts the program short. Using just char*[] (or even string*[], ugh) at least allows you to end the array with NULL (which is distinct from \"\").
  
  

  Quote:

  
  

      LetterStrings a, b;
  

  
  

  
  Nitpicking: unused b.
  
  

  Quote:

  
  isalpha is obviously better then my check via ASCII-Table codes (I've edited my solution), but the top-solutions seems to include quite a lot which isn't needed.

  
  Yeah, I think that's just a bunch of standard stuff that author includes in every file.

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• 10/16/2024 13:00

  moose 00

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  Thanks.
  
  Now my next questions:
  As a python programmer I'm used to have integers which are always as big as I need them. In C++ the biggist \"standard int\" type seems to be \"unsigned long long\" which is in [0;9223372036854775807] which is [0;2^63-1].
  What do I do if I need longer integer types?
  
  How do I convert an unsigned long long to a string?

  Edited by moose 09/08/2011 09:02 ago

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• 10/16/2024 13:00

  dloser 00

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  You'll probably want to use one of the available libraries for that (e.g. GMP).

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