C++ Implementation of String Matching Algorithm

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"

Returns "Justin4" since Justin and Justin with the numbers 1 through 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:

1. 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.

2. How do you concatenate an int and a string? In Java it was as simple as using the + operator.

3. In my main function, it says there is no matching function call for Username::NewMember(std::string, std::string). hy 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

There are 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 your 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 your Username class. It is not correct in C/C++. Unlike Java, the main function has 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 anyway:

string newMember(string* existingNames, const string& newName);
//                                      ^^^^^       ^

Are you sure you need something allocated dynamically in the main function?