i dont what is the problem in this simple program plz help distinguish prime numbers

n=input ('the num ');
if n==1 ;
    disp('the num is prime ')
    break
else 
    for i=n:sqrt(n);
        if rem(n,i)==0;
            disp('the num is not prime ')
        else
            disp('the num is prime')
        end
    end
end

[the cyclist]

One side comment: 1 is not generally considered a prime. See, for example, http://en.wikipedia.org/wiki/Prime_number.

Answer 1

[the cyclist]

Two errors I see:

Your "break" statement should be a "return" statement.

Where you have

for i=n:sqrt(n)

you should have

for i=2:sqrt(n)

I think.

When you make those changes, you actually get into your for loop properly, and you will then see that your algorithm is flawed. :-(

[malek ebrahem]

ok thnx there is another problem but not technical its in the idea anyway i made another i find another successful program num=input('the num '); j=0 if num~=0 for i=2:sqrt(m); if rem(n,i)==0; j=j+1; end end if j~=0; disp('the num is not prime'); else disp('the num is prime') end else('num is prime') end

Answer 2

[Sean de Wolski]

if isprime(num)
  disp('The num is prime')
else
  disp('The num is not prime')
end

[malek ebrahem]

thnx i tried to make program without built in function