How to show non prime numbers (what is the contrari function of prime?)

clc
clear all

n=input('number')                 % Natural number that you want to know if it a prime number
i=2;
x=[];

if n==0 | n==1
    disp('there are not prime numbers');
end

while i<=sqrt(n)

      if rem(n,i)==0    %In this part i want to show the non prime numbers (i don't know the function name)     
          x=n

      else              %In this part i show the prime numbers

          y=primes(n)

          break
      end

      i=i+1;
  end

fid=fopen('Prime_numbers.txt','w');    %In this final part i create a .txt document for save the prime       
fprintf(fid,'%2d\t%2g\t',y);
fclose(fid);

fid=fopen('Non_prime_numbers.txt','w'); %In this final part i create a .txt document for save the non prime 
fprintf(fid,'%2d\t%2g\t',x);
fclose(fid);

Answer 1

[Walter Roberson]

You could use setdiff() of the range of values, asking to remove the primes.

[Toni Clares]

%Thanks i tried but i don't know the right way to use it

clc
clear all

n=input('number')                 % Natural number that you want to know if it a prime number
i=2;
x=[];

if n==0 | n==1
    x=n;
end

while i<=sqrt(n)

      if rem(n,i)==0
          x=n

      else
          z=1:n
          y=primes(n)
          x=setfdiff(z,y)  % I don't know how to use it

          break
      end

      i=i+1;
  end

fid=fopen('Prime_numbers.txt','w');
fprintf(fid,'%2d\t%2g\t',y);
fclose(fid);

fid=fopen('Non_prime_numbers.txt','w');
fprintf(fid,'%2d\t%2g\t',x);
fclose(fid);

[Toni Clares]

I sort out!!!

clc
clear all

n=input('number')                 % Natural number that you want to know if it a prime number
i=2;
x=[];

if n==0 | n==1
    x=n;
end

z=1:n;
y=primes(n)
x=setdiff(z,y)

fid=fopen('Prime_numbers.txt','w');
fprintf(fid,'%2d\t%2g\t',y);
fclose(fid);

fid=fopen('Non_prime_numbers.txt','w');
fprintf(fid,'%2d\t%2g\t',x);
fclose(fid);