C Algorithm to Show n is a Prime Number

[Dinesh Kumar bca]

Hai...I am a very basic student for C...So many apologies for asking this basic question. My question is, How to write algorithm for the program to given n number is prime number? Please help.......

[weaknessforcats]

Have you tried Google on this?

[whodgson]

As you know a prime number is one which can only be divided by 1 or itself.
So (ignoring these two) if the number can be divided by 2,3,5,7,9...... ...etc it is not prime. If not it is prime. I think that is the algorithm for determining whether a number is prime or not. Could you write some code to reflect this algorithm?
e.g.

 if(n%2==0)cout<<"n is not prime"<<endl;

[JosAH]

 if(n%2==0)cout<<"n is not prime"<<endl;

Nitpick: what about n == 2?

kind regards,

Jos

[whodgson]

Yep, as everyone knows 2 is the only even prime

[mstab]

a basic solution is as follows,

this in not optimised, ie very inefficient, can be improved considerably
an lends itself to a recursive solution.

Code removed per posting guidelines

[newb16]

You do not need dividers greater thatn sqrt(n) to check.
let alone that this loop will execute only once for odd N. ( 0==ret )