CODEWITHSUNDEEP
c++arraysstringduplicates
Ataur Rahman Chowdhury
Ataur Rahman Chowdhury

Reputation: 43

how to avoid duplicate entry in array of string?

in my small project i want to make small program where I have to store unlimited no of unique string, but user can input same unique string multiple times. But in my array I want only unique id to be saved only once. In simple word I dont want duplicate data in my array. I want to do this in C++, But somehow I cant get the logic ? Can someone please help me out here?

#include <stdio.h>
#include <iostream>
#include <string>

    using namespace std;

    int main(){

        string str[100],ch;
        int i,j,n;
        j=0;n=0;
        //str[0]= "a";

       do {
         getline(cin,ch);
         for (i=0;i <j; i++){
         if (ch=str[i]){
                        cout << "duplicate" ;
                        }
         str[i] =ch;
         j++;
         }
         n++;
           } while (n =100);
        getchar();

    }

I am noob at C++, so please help me out here

Upvotes: 1

Views: 4963

Answers (3)

AndersK
AndersK

Reputation: 36082

haven't compiled this but something like this should work, that said you should use a set or similar more c++sh ways of solving this if you want a more efficient solution but from the sound of it you seem to need more basic advice.

int main()
{
    const int maxstrings = 100; // never use magic numbers, instead declare them as a constant
    string str[maxstrings],ch;  // should have other variable names that are more descriptive
    int i,n = 0; // didn't see the need for j here, n contains number of unique strings

    do 
    {
      getline(cin,ch);
      // you may want to check what is in ch first, to see if user doesn't want to enter 100 strings           

      bool duplicate = false;

      for (i=0; !duplicate && i<n; ++i) // check among number of stored strings (n)
      {
        if (ch==str[i]) // use two '=' for equality i.e '=='
        {
          cout << "duplicate:" << ch << endl; // show the duplicate, user friendlier
          duplicate = true;
        }
      }
      // did we find a duplicate? no, then add to array
      if ( !duplicate )
      {
        str[n++]=ch;
      }
   } 
   while ( n < maxstrings );
   getchar();

}

Upvotes: 2

John Dibling
John Dibling

Reputation: 101456

If you want to maintain a list of unique strings, then the easiest thing to do is use the right tool for the job; namely, a set<string> rather than an array of string.

Edit:

If you don't need your collection of strings to be sorted (as set does), and you have it available to you, it would be more appropriate to use unordered_set rather than set. set will just do needless sorting every time you add a string.

Edit2:

A set is an associative array, which means there can only be one element with a given key. In the case of set<string>, the key is the string you insert. If you insert the same key multiple times, there will still only be one instance of it in the set.

Here's an example program that illustrates this. If you run this you'll find the output is just one "foo", even though "foo" was inserted 3 times:

#include <set>
#include <string>
#include <iostream>
#include <algorithm>
#include <iterator>
using namespace std;

int main()
{
    set<string> my_strings;

    my_strings.insert("foo");
    my_strings.insert("foo");
    my_strings.insert("foo");

    copy( my_strings.begin(), my_strings.end(), ostream_iterator<string>(cout, "\n"));
}

Upvotes: 7

webbi
webbi

Reputation: 851

You should use a vector-like to keep a list of strings. For example you can use a set (http://www.cplusplus.com/reference/stl/set/).

Besides that, if you need to check if the string already exist on the set<> object, then you need to check for it using find() method: http://www.cplusplus.com/reference/stl/set/find/

I think that's all you need.

FYI: the line: if (ch=str[i]){ is totally wrong! you are not comparing ! you are assigning, remember to use '==' and not '='.

Upvotes: 0

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