Remove consecutive duplicate values in a string

Question

I am trying to make a program so that when a string such as "cccaaaattt" is entered the output will be "cat"

Here is my code so far:

#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;
int main(array<System::String ^> ^args)
{
 string str = "";//create an empty string variable named str
 std::cout << "What word do you want to remove duplicate characters from?";
 cin >> str; //fill the str variable with the word the user whants to remove duplicate consecutive characters from
 char current;//create a new char variable named current
 char lastChar;//create a new char variable named lastChar for the previos character in the string
for (int i = 1; i < str.length(); i++){ //iterate through until it reaches the end of the string
 lastChar = str[i - 1]; //set lastChar to the previos char in the string
 current = str[i];//set current to the current char in the string
 if (lastChar == current){//if the lastChar and the current are equal (the string has two consecutive characters
 str.erase(i,1);//erase the current character
 }
}
cout << str << endl; //display the new string
system("pause");
return 0;

}

I commented on what I thought the code would have done.

It does not remove the right amount of character making my output "ccaatt"

Thanks for the help.

• MSalters: I started retagging it as C++/CLI but tbh it's almost pure C++ except for args (which is unused)
• MSalters: Hint: when you have 4 consecutive identical characters, you have 2 pairs. You correctly remove the second half of each pair.

Answer 1

One extremely easy and efficient way to do this in C++ is to use std::unique from the algorithm library and the erase function of std::string.

#include <iostream>
#include <string>
#include <algorithm>
int main()
{
 std::string x("xxbbbbccccczzzzxxxx");
 x.erase(std::unique(x.begin(), x.end()), x.end());
 std::cout << x << "\n";
}

This will output:

xbczx

• TroyStacer: I new there would be something simple like this. Thank you. Your user name is relevant :)

Answer 2

Whereas using std::unique does the job, your error is that you increase your counter after erase. The fixed implementation:

for (int i = 1; i < str.length(); /* No increment here */ ) {
 if (str[i - 1] == str[i]) {
 str.erase(i, 1);
 } else {
 ++i;
 }
}