Method push_back

CPP/vector-concepts/vector.h:11–24

        arr= new int[ms];
    }
    void push_back(int d){
        if(cs==ms){
            int *oldArr=arr;
            ms*=2;
            arr= new int[ms];
            //copy the old items to the new array of double size
            for (int i = 0; i < cs; i++) {
                arr[i]=oldArr[i];
            }
            delete []oldArr;
        }
        arr[cs]=d;
        cs++;
    }
    void pop_back(){
        if(cs>=0){
            cs--;