Using a While Loop to find Prime Values

Abraham Robledo

2019 2 7

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How can I crate a program that display rather tha verifies umbers that are prime? I tried

x=23;

y=2;

while rem(x,y)~=0

y=y+1;

end

if y==x

disp('Prime');

else

disp('Not Prime');

end

but it this only shows prime and not prime. I am trying to use a while loop. Serious answers please.

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Preethi 2019-2-8

Are you providing a set of numbers as input and you want to display prime numbers?

Sarah Crimi 2019-2-8

在 MATLAB Online 中打开

This is code to find the first 20 prime numbers.

%Create a list of first 200 numbers.
x = 1:200;
x = x';
%Preallocate for primes vector.
primes=zeros(200,1)
%Preset the counter to 2 and prime_numbers to 0.
counter = 2;
prime_nums = 0;
  while(prime_nums<20)
%     
    %x(counter) is the number that will be tested.
    num = x(counter)
    flag = 0;
    
    for i = 2:(num-1)
       a = mod(num,i) ;
       if a==0
           flag = flag + 1; %Update flag when item is divisable by a number prior to it that is not 2 or greater.
       end
    end
    
    %If the item is divisable by a number prior to it that is 2 or greater, it is not a prime.
    if(flag>0)
        
        primes(counter-1,1)=0;
    else
        %If the item is not divisable by a number prior to it that is 2 or greater, it is a prime.
        prime_nums = prime_nums +1;
        primes(counter-1,1) = num;
    end
    
    %Update counter to move to next item in list.
    counter = counter+1
  end
 
  %Get the nonzeros from primes vector to get the first 20 primes. 
  result=nonzeros(primes);
  
  %Display results.
  disp(result)