determine prime number

[teng125]

can smby give me a simple example algorithm to determine whether the number is prime or not such as using while loop, if.....then......else or others which is simple

thanx

[berkeman]

Google can be a helpful tool to get familiar with, Teng. I simply googled pime number calculation program example, and got lots of good hits. Just check out one of the top hits in the list:

http://www.google.com/search?hl=en&q=prime+number+calculation+program+example

[teng125]

but I'm looking for a simple example about prime number determination [algorithm] for programming language only using if.....then... or while loop or repeat loops..... that describe the steps of calculation

[berkeman]

but I'm looking for a simple example about prime number determination [algorithm] for programming language only using if.....then... or while loop or repeat loops..... that describe the steps of calculation
How many of those google hits did you actually look through?

[buddyholly9999]

A simple example I can think of is go through every integer between 1 and the prime number you want to test and check to see if it is a divisor.

[a_ramage_1989]

A simple example I can think of is go through every integer between 1 and the prime number you want to test and check to see if it is a divisor.

you only need to go up to a third of the number. This is because if it is even then you know it is not prime, unless it is two. odd numbers are not divisble by 2, so the next divisor would be 3.

[shmoe]

you only need to go up to a third of the number. This is because if it is even then you know it is not prime, unless it is two. odd numbers are not divisble by 2, so the next divisor would be 3.

It's enough to go up to the square root of the number, much more efficient than having to check up to a third (still not at all fast though).

[rbj]

and you only need to test (up to the \sqrt{N} ) the odd numbers that are not known multiples of other prime numbers (like multiples of 3, 5, 7, 11, 13, etc). if your programming language has a remainder operator (like the "%" operator in C and C++), you can use that to test a candidate factor to see if it divides evenly into N. but if you don't, you have to divide, use the floor() or int() operator to get the integer part of the quotient, subtract the integer part from the quotient and, if that result is zero, it divides evenly.

if all candidate factors fail to divide evenly into N, then N is prime. if any one candidate factor divides evenly into N, it is not prime.

[teng125]

okok........thanx