strtoul() function use
 

OK, I finally figured out command line arguments... my program is called prime, in the console i need to type "prime 7" and the program will tell me if its a prime or not.

heres my code:

#include <cstdlib>

#include <iostream>

#include <iomanip>

#include <stdlib.h>



using namespace std;





int main(int argc, char *argv[])

{

   const unsigned long arraySize = 1000000;

   bool a[arraySize];

   unsigned long num1;

   unsigned long num2;

   unsigned long num3;

   unsigned long counter = 0;

   unsigned long primes = 0;

   char z;

   unsigned long answer = 0;

  

//Initializing elements to 1 

        

for (int i = 0; i < arraySize; i++)             

{

   a[i] = 1;

}       

// For array subscript 2, all elements beyond 2 in the array that

// are multiples of 2 will be set to zero ; for array subscript 3, 

// all elements beyond 3 in the array that 

// are multiples of 3 will be set to zero





for (int i = 2; i * i < arraySize; i++)

{

    if (a[i])

       for (int j = i + i; j < arraySize; j += i)

          a[j] = 0;

} 

// if user enters more than 3 numbers or 0 numbers

// program should output useful information

// and title and author



if ((argc > 4) || (argc == 1))

{

 cout<<"This is Programming Assignment #5"<<endl;

 cout<<"THE SIEVE OF ERATOSTHENES"<<endl;

 cout<<"by Jeremy Rice"<<endl;

 cout<<endl;

 cout<<"Usage:"<<endl;

 cout<<"\tprime num1 - determines if num1 is a prime"<<endl;

 cout<<"\tprime num1 num2 - displays primes between numbers."<<endl;

}



// if user enters one number

// program should determine if that number is a prime



if (argc == 2)

{  

   if (a[argc] == 1)

   {   

       num1 = strtoul(argv[]);

       counter++;

       cout<<"This is a prime number."<<endl;  

   }

   else

   cout<<"This is not a prime number."<<endl;

}







// if user enters 2 numbers

// program, should calculate the prime numbers 

// between the two numbers



if (argc == 3)

   {

         

   }







return EXIT_SUCCESS;

}

heres the part I need help with

// if user enters one number

// program should determine if that number is a prime



if (argc == 2)

{  

   if (a[argc] == 1)

   {   

       num1 = strtoul(argv[]);

       counter++;

       cout<<"This is a prime number."<<endl;  

   }

   else

   cout<<"This is not a prime number."<<endl;

}

what do I put in the num1 = strtoul(argv[]) to take the number entered in the command line prompt?

Re: strtoul() function use
 

A contradiction!

Re: strtoul() function use
 

If you enter prime 7 as the command-line argument then the word prime will be in argv[1] and '7' is in argv[2], making argc == 3, not 2. argv[0] is almost always the name of the executable program.

Re: strtoul() function use
 

I don't know about the stroul function.

I also have no idea what you are planning to do with this.

if (argc == 3)

   {

         

   }

Let me try. arg[0] refers to the name of exe, which is tprime over here. Then onwards, arg[r] refers to the rth command line argument.

Re: strtoul() function use
 

You will have to convert these strings containing numbers to integers by an appropriate function.

Re: strtoul() function use
 

Oops! Ancient Dragon & I replied just at about the same time!!

Re: strtoul() function use
 

Ok, so this is what i have... sorry for the ignorance, but i am slowly getting it..

if i typed "prime 45 70"
the program rightly displays primes between 45 and 70..
if I type "prime" the program rightly displays who it was created by and how to use it...except with a "memory fault"at end.

If I type " prime 6" I just get "memory fault" it should display if that number is prime or not..

What am i doing wrong to get that memory fault.. That is the last thing I need to do with this program, again sorry, but thank you for patience and your help.

#include <cstdlib>

#include <iostream>

#include <iomanip>

#include <stdlib.h>



using namespace std;

const unsigned W = 10;



int main(int argc, char *argv[])

{

   const unsigned long arraySize = 1000000;

   bool a[arraySize];

   unsigned long num1;

   unsigned long num2;

   unsigned long num3;

   unsigned long counter = 0;

   unsigned long primes = 0;

   char z;

   unsigned long answer = 0;

  

//Initializing elements to 1 

        

for (int i = 0; i < arraySize; i++)             

{

   a[i] = 1;

}       

// For array subscript 2, all elements beyond 2 in the array that

// are multiples of 2 will be set to zero; for array subscript 3, 

// all elements beyond 3 in the array that 

// are multiples of 3 will be set to zero





for (int i = 2; i * i < arraySize; i++)

{

    if (a[i])

       for (int j = i + i; j < arraySize; j += i)

          a[j] = 0;

} 

// if user enters more than 3 numbers or 0 numbers

// program should output useful information

// and title and author



if ((argc > 4) || (argc == 1))

{

cout<<"This is Programming Assignment #5"<<endl;

cout<<"THE SIEVE OF ERATOSTHENES"<<endl;

cout<<"by Jeremy Rice"<<endl;

cout<<endl;

cout<<"Usage:"<<endl;

cout<<"\tprime num1 - determines if num1 is a prime"<<endl;

cout<<"\tprime num1 num2 - displays primes between numbers."<<endl;

}







num1 = atoi(argv[1]);

num2 = atoi(argv[2]);

num3 = num1;

// if user enters one number

// program should determine if that number is a prime



if ((argc > 1) && (argc < 3))

{

   if (a[num1] == 1)

   cout<<num1<<" is a prime number."<<endl;

   else

   cout<<num1<<" is not a prime number."<<endl;

}



// if user enters 2 numbers

// program, should calculate the prime numbers 

// between the two numbers



if (argc == 3) 

   for (int i = num1; num1 < num2; num1++)



    if (num1 < num2)

    if (a[num1] == 1)

     {

      counter++; 

      cout<<setw(W)<<num1;

     }

       else if

        (a[num1] == 0)

     {

         cout<<"";

     }   

        else 

          cout<<"num1 must be lower than num2."<<endl;          

if (num1 > num2)

{

cout<<"Error: Invalid user specified number."<<endl;

return 0;

}

cout<<endl;

cout<<"There are "<<counter<<" primes between "<<num3<<" and "<<num1<<endl;

return EXIT_SUCCESS;

}

Re: strtoul() function use
 

Between lines 51 and 52 you need to add return EXIT_SUCCESS;. (If you start your code blocks with the name of the language you are using, you get line numbers: [code=C++].)

Line 56: are you sure there is an argv[ 1 ]?
Line 57: are you sure there is an argv[ 2 ]?
Line 62: isn't that the same as if (argc == 2) ?
Line 90: you could just swap the numbers so that num1 < num2...

A few other notes. Choose C or C++, not both:
1. Use #include <cstdlib>
2. When dealing with boolean values, use the keywords true and false, so it is obvious that you are dealing with a boolean value and not an integer.
3. Likewise, when testing boolean values, say
if (a[num1])
or
if (a[num1] == true)
4. Stick lines 43..52 as the first thing in your main. (There are good reason's why, but I don't want to take the time to explain them all now...)
5. Use functions.
6. Old C people and those who don't know better like to have their students use const int foosize = 12000; and junk like that. That's really about the same thing as saying: #define foosize 12000
The better way is just to declare your array as bool a[1000000]; and use the sizeof operator to get its size later:
for (int i = 0; i < sizeof( a )/sizeof( a[ 0 ] ); i++)
Well, it is another way, at least. (It prevents you from being tempted to do dumb things.)
7. You forgot to use strtoul()...

You seem to have a pretty good grasp of what your code should be doing. Good job.

Hope this helps.