Dev - C++ - Caracteres iguales

#include <iostream>

using namespace std;

int main ()

{

char a,b;

cout<<"Introduce los caracteres: ";

cin>>b;

cin>>a;

    while(a!=b);{

    cout<<"Has introducido dos caracteres iguales"<<endl;}

return 0;

}

#include <iostream>

using namespace std;

int main () {

    char a, b;

    cout << "Introduce los caracteres: ";

    cin >> a;

    cin >> b;

    while ( a == b ){

        cout << "Has introducido dos caracteres iguales" << endl;

    }

    return 0;

}

#include <iostream>

#include <string.h>

using namespace std;

int main () {

    string str;

    cout << "Introduce los caracteres: ";

    cin >> str;

    for (int i =0; i  < str.length()-1 && str.length() >=2; i++){

        if (str[i] == str[i+1]){

            cout << "Has introducido dos caracteres iguales" << endl;

            break;

        }

    }

    return 0;

}

#include <iostream>

#include <string.h>

using namespace std;

int main () {

    string str;

    cout << "Introduce los caracteres: ";

    cin >> str;

    int i=0;

    while (i  < str.length()-1 && str.length() >=2){

        if (str[i] == str[i+1]){

            cout << "Has introducido dos caracteres iguales" << endl;

            break;

        }

        i++;

    }

    return 0;

}

#include <iostream>

#include <string.h>

using namespace std;

int main () {

    char str[50];

    cout << "Introduce los caracteres: ";

    cin >> str;

    int i=0;

    while (i  < strlen(str)-1 && strlen(str) >=2){

        if (str[i] == str[i+1]){

            cout << "Has introducido dos caracteres iguales" << endl;

            break;

        }

        i++;

    }

    return 0;

}