c++ implementation of string matching alg - c++

Question

I am implementing a String matching algorithm for a username database. My method takes an existing Username database and a new username that the person wants and it checks to see if the username is taken. if it is taken the method is supposed to return the username with a number that isn't taken in the database.
Example:
"Justin","Justin1", "Justin2", "Justin3"
Enter "Justin"
return: "Justin4" since Justin and Justin with the numbers 1 thru 3 are already taken.
I have already written this code in Java, and now I am writing it in C++ for practice. I have a few problems though:
How do you compare two strings? I have tried strcmp and a few others but I always get the error message: cannot convert std::string to const char* for argument 2.
how do you concatenate an int and a string? in java it was as simple as using the + operator.
In my main function, it says there is no matching function call for Username::NewMember(std::string, std::string). why does it not recognize newMember in main?
#include<iostream>
#include<string>
using namespace std;
class Username {
public:
string newMember(string existingNames, string newName){
bool found = false;
bool match = false;
string otherName = NULL;
for(int i = 0; i < sizeof(existingNames);i++){
if(strcmp(existingNames[i], newName) == 0){
found = true;
break;
}
}
if(found){
for(int x = 1; ; x++){
match = false;
for(int i = 0; i < sizeof(existingNames);i++){
if(strcmp(existingNames[i],(newName + x)) == 0){
match = true;
break;
}
}
if(!match){
otherName = newName + x;
break;
}
}
return otherName;
}
else return newName;
}
int main(){
string *userNames = new string[4];
userNames[0] = "Justin";
userNames[1] = "Justin1";
userNames[2] = "Justin2";
userNames[3] = "Justin3";
cout << newMember(userNames, "Justin") << endl;
delete[] userNames;
return 0;
}
}

Answer 1

Ok, there is some mistakes in your code :
If you want to compare two strings, simply use the operator== : string == string2
If you want to append an int to a string in C++ you can use streams :
#include <sstream>
std::ostringstream oss;
oss << "Justin" << 4;
std::cout << oss.str();
You are passing a string* to the function newMember but you prototype doesn't match that :
string *userNames = new string[4];
newMember(userNames, "Justin"); // Call
string newMember(string existingNames, string newName); // Protype
I think it should be : string newMember(string* existingNames, string newName); no ?
In the example, your main function is inside you class Username. It is not correct in C/C++. Unlike Java, the main function as to be in the global scope.
Finally you should use const-reference parameter because you don't need to modify the content of them and you need to copy them either :
string newMember(string* existingNames, const string& newName);
// ^^^^^ ^
Are you sure you need something allocated dynamically in the main function ?