I don't understand how arrays can help me to reduce the size of the void loop code though.
Put the pin numbers in an array
Put the character corresponding to each pin in a second array
Use a for loop to read each input in turn.
When you find that an input has gone HIGH use the pin number array index to get the corresponding character from the character array and output it
NOTE : you could use an array of structs instead of 2 arrays but I don't think that you are ready for that yet.