Programming Forums > Application Development > C++

BehemothPhoenix · Mar 19th, 2005, 6:40 PM

Basically, I have to write a program for school, in which I have to determine whether a user inputted value is prime or not. I also have to write another program determining what factors of an inputted value are prime. I've tried everything (and we can't use the math.h library). I'm really not too sure what to do, and any help you could give me would be greatly appreciated!!

Edit: I don't really need a whole program, just an idea of where to start.

gardon · Mar 19th, 2005, 11:12 PM

hmmm... well a long way would be to incorporate all the prime numbers into a function, and if it matches that in the function then it's prime (from the number the user entered)

really long time to make something like that, or...

cheat and write the mat.h library header into a function and use it in your assignment

Mjordan2nd · Mar 20th, 2005, 12:55 AM

It's not a tough program at all. Write a function to determine whether it's prime or not. In the function, have an int variable which stores whether the number is prime or not -- 1 for prime and 0 for not prime. Initialize it to 1. Have it run through a loop from 2 up to 1 below the number you're testing for. If it's evenly divisible, then set the value to 0 . . .

(Toggle Plain Text)

 
 #include <stdio.h>
 
 #define PRIME 1
 #define NOT_PRIME 0
 
 int main(void)
 {
 	 // some code
 	 // ...
 	 // ...
 	 int isPrime = checkPrime(number);
 }
 
 int checkPrime(int num)
 {
 	 int value = PRIME;
 	 int i = 2;
 	 for(i; i<num; i++)
 	 {
 		  if(i%num==0)
 			   value = NOT_PRIME;
 	 }
 	 return value;
 }

gardon · Mar 20th, 2005, 2:06 PM

I didn't know what the call for prime numbers were, that's why I couldn't write the prog.

Mar 19th, 2005, 6:40 PM	#1
BehemothPhoenix Newbie Join Date: Mar 2005 Posts: 1 Rep Power: 0	Help with a couple prime numbers programs!! Basically, I have to write a program for school, in which I have to determine whether a user inputted value is prime or not. I also have to write another program determining what factors of an inputted value are prime. I've tried everything (and we can't use the math.h library). I'm really not too sure what to do, and any help you could give me would be greatly appreciated!! Edit: I don't really need a whole program, just an idea of where to start.

Mar 20th, 2005, 12:55 AM	#3
Mjordan2nd The Supreme Ruler Join Date: May 2004 Location: Houston Posts: 1,476 Rep Power: 6	It's not a tough program at all. Write a function to determine whether it's prime or not. In the function, have an int variable which stores whether the number is prime or not -- 1 for prime and 0 for not prime. Initialize it to 1. Have it run through a loop from 2 up to 1 below the number you're testing for. If it's evenly divisible, then set the value to 0 . . . (Toggle Plain Text) #include <stdio.h> #define PRIME 1 #define NOT_PRIME 0 int main(void) { // some code // ... // ... int isPrime = checkPrime(number); } int checkPrime(int num) { int value = PRIME; int i = 2; for(i; i<num; i++) { if(i%num==0) value = NOT_PRIME; } return value; } #include <stdio.h> #define PRIME 1 #define NOT_PRIME 0 int main(void) { // some code // ... // ... int isPrime = checkPrime(number); } int checkPrime(int num) { int value = PRIME; int i = 2; for(i; i<num; i++) { if(i%num==0) value = NOT_PRIME; } return value; } __________________ "Every gun that is made, every warship launched, every rocket signifies, in the final sense, a theft from those who hunger and are not fed, from those who are cold and are not clothed. The world in arms is not spending money alone. It is spending the sweat of its laborers, the genius of its scientists, the hopes of its children." - Dwight D. Eisenhower

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Mar 19th, 2005, 11:12 PM	#2
gardon Programmer Join Date: Dec 2004 Posts: 87 Rep Power: 4	hmmm... well a long way would be to incorporate all the prime numbers into a function, and if it matches that in the function then it's prime (from the number the user entered) really long time to make something like that, or... cheat and write the mat.h library header into a function and use it in your assignment

Mar 20th, 2005, 2:06 PM	#4
gardon Programmer Join Date: Dec 2004 Posts: 87 Rep Power: 4	I didn't know what the call for prime numbers were, that's why I couldn't write the prog.

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Programming Forums > Application Development > C++

Help with a couple prime numbers programs!!