How can I create a loop that doesnt allow the same number to be input twice?

I have this code, that when passed a variable, creates a matrix and lets you input digits for a magic square

function magicsquare(M)

Code:

clc
[r,c] = size(M); 
    if (r ~= c)  
        disp('These are not the dimensions of a square!\n');
    else
        cSum = sum(M); 
        rSum= sum(M'); 
        d1= sum(diag(M)); 
        d2= sum(diag(fliplr(M))); 
        if(isequal(d1,d2,cSum(1),rSum(1)) && isequal(cSum,rSum)) 
            fprintf('This square is magic!\n')
        else    
            fprintf('This is not a magic square!\n')
        end    
    end
end

How can I edit this to make it to where the user cannot input the same digit twice when inputting their numbers for the magic square?

Thanks

Answer 1

[Walter Roberson]

if length(unique(M)) ~= numel(M)
    error('You entered some number twice')
end