Someone please help me with combination lock

Player enterring to trigger and canvas actvated, and i need entering 4 number to "open the door". So i make 4 canvas with ten numbers, them i tapped on button this keypad makes don`t visible and next makes visible, when I enterring 4 keypad, i need to press ok. And on screen must visible label "wrong" or "correct" password it work(example of code)

 public void checkcode() //attached to button
     {
         if(a == 1)
         {
             if(b == 2)
             {
                 if(c == 3)
                 {
                     if(d == 4)
                     {
                         //when code correct
 
                     }
                 }
             }
         }
         if(a != 1)
         {
             if(b != 2)
             {
                 if(c != 3)
                 {
                     if(d != 4)
                     {
                         //when code wrong
                     }
                 }
             }
         }
     }

variable takes the value of Button (UI)

 `    public void but6()  //pulic func be attched to button 
     {
         keys1.enabled = false; 
             keys2.enabled = true;
         a = 6;   //value of varible
     }`

I would like to then i press some button i can see which button i press previously. For example i press three buttons and can see which, first is 1, second 2 etc. How i can in. I need only creating 4 rows of 10 numbers, and manage it on script, or something other way plz with using C#