how to make a for loop that adapts to vector size?

Im currently making a program that will return the values of 3x+1 given starting value x.

Here is the trimmed code.

                        //3x+1
                        //starting at any positive integer (x)
                        //multiply by 3 then add one
                        //(n%2==0?/2:3n+1)

                        std::vector<int> Holder;
                        int usrNum;
                        std::cin >> usrNum;
                        
                        Holder.push_back(usrNum);
                        Holder.push_back(3*usrNum+1);

                        for(int i = 1; i < 200; i++){
                            (Holder[i]%2==0?Holder.push_back(Holder[i]/2):Holder.push_back(3*Holder[i]+1));
                        }
                        
                        for (int i = 0; i < Holder.size(); i++) {
                            std::cout << Holder[i] << " ";
                        }
                        

currently im using 200 as a hard coded value because if i use i < Holder.size() it causes an infinite loop and i never catches up.

anyone have any ideas as to how i can make it loop until it reaches the value 1?

>Solution :

Use a while loop, with the termination condition being when the last element is 1. Have a look at this reference for std::vector for help.