can anyone help me?
With what? If you know which pins on the keypad are row pins and which are column pins, using the keypad library to get which key is actually pressed is trivial.
Storing the keys in an array, as you discover that they are pressed, is pretty easy. Detecting that the key that was pressed is a 'C', so that, instead of storing it in the array, you use the data in the array, is dirt simple.