The way you've written this, your program checks for this first
(p1 == 's')
so, seeing that you've selected "s" it will always defualt to that. You should use the lower() function in a case like this. That way, if the input is "S" or "s", your output will always be "s". It's easier to compare that way.
p1 = input('Player 1 Play:\n','s');
p2 = input('Player 2 Play:\n','s');
if strcmp(lower(p1),'p') && strcmp(lower(p2),'r')
fprintf('Player 1 wins the game because paper cover rock');
elseif strcmp(lower(p1),'s') && strcmp(lower(p2),'p')
fprintf('Player 1 wins the game because Scissor cut paper');
elseif strcmp(lower(p1),'s') && strcmp(lower(p2),'r')
fprintf('Player 2 wins the game because Rock break scissor');
else %after you finish writing all the rest of the elseif statements out
fprintf('Entry must be r, p, or s')
end
