Wrong User Input - c++

Question

So I'm making a card game using C++ and I'm doing some basic user input, but I am wondering how to handle wrong user input such that you can retry without terminating the program and I'm not sure how to do that.
#include <iostream>
#include <string>
#include <stdio.h>
#include <ctype.h>
#include <algorithm>
using namespace std;
int main()
{
string command;
int i = 0;
char c;
string test1 = "help";
string test2 = "start";
cout<< "Welcome to My Card Game" << "\n";
cout<<"\n";
cout<< "For Rules please type 'rules'" << "\n";
cout<<"\n";
cout<< "To Play please type 'start'" << "\n";
getline(cin, command);
transform(command.begin(), command.end(), command.begin(),::tolower);
if(!command.compare(test1)){
cout << "You typed help" << "\n";
return 0;
}
if(!command.compare(test2)){
cout << "You typed start" << "\n";
return 0;
}
else{
cout << "Not a valid command" << "\n";
return 0;
}
}
EDIT: Solved with a simple while loop wrapped around the if-else statements.

Answer 1

You do not necessarily have to end the program at every single 'if'.
Also the '!' operator in your if statements is unnecessary, since it checks for inequality rather than equality.
You can try looping the program, which will make it restart if a user types in an invalid command, in your case:
#include <iostream>
#include <string>
#include <stdio.h>
#include <ctype.h>
#include <algorithm>
using namespace std;
int main() {
string command;
int i = 0;
char c;
string test1 = "help";
string test2 = "start";
cout<< "Welcome to My Card Game" << "\n";
cout<<"\n";
cout<< "For Rules please type 'rules'" << "\n";
cout<<"\n";
cout<< "To Play please type 'start'" << "\n";
while (1) {
getline(cin, command);
transform(command.begin(), command.end(), command.begin(), ::tolower);
if(command.compare(test1)){
cout << "You typed help" << "\n";
//continue code for when they type help.
}
else if (command.compare(test2)) {
cout << "You typed start" << "\n";
//continue code for when they type start.
//make sure that you break the while loop with 'break;' when they finish the game so that your program will end.
}
else {
cout << "Not a valid command" << "\n";
};
};
return 0;
};
I hope this helped.