Algorithm isPrime

   //read a single value from the user and print whether it is prime

   //prompt and read pp (potential prime)
   print "enter potential prime > 1: "
   read pp
   
   //initialize pd
   pd = 2
   //check for potential divisors of pp
   while(pp % pd != 0)
        pd++

   //print result
   if(pp == pd)
        print pp, " is prime. "
   else
        print pp, " is composite. "
   fi

   //alternate way to print
   //print pp, ((pp == pd) ? "is prime " : "is composite")

End .

Exercises

1. Translate the above algorithm into a c++ program, isPrime-v1.cpp.
   
   isPrime-v1.cpp
   
   
2. Modify isPrime-v1.cpp by adding an EOF-controlled while loop to generate this I/O interface:

   enter n > 1 (c-d to exit): 5
   5 is prime
   enter n > 1 (c-d to exit): 4
   4 is composite
   enter n > 1 (c-d to exit): ^d
   exiting . .
   

   w1/isPrime-eof.cpp

3. Write a c++ function that meets this specification:
   
   

   /* isPrime() ----------------------------------------------
    * returns true iff n is prime */
   int isPrime(long n);
   

   
   Remember: Functions do not use cin and do not use cout. The function returns a value to the caller (main(), for example), and the caller will handle I/O.
   
   Modify isPrime-v1.cpp so that main() calls function isPrime().

   ../w4/isPrime-v2.cpp
   

4. Function definitions can be placed in their own header file and then #included in a client program. Example:

   ../w5/isPrime-fn1.h      --header file
   ../w5/isPrime-fn2.h      --header file
   ../w5/isPrime-v3.cpp   --client (#includes one of the header files)

5. Write a pseudocode algorithm to meet this I/O spec:

   enter n > 1 (c-d to exit): 5
   first prime greater than 5 is 7
   enter n > 1 (c-d to exit): 11
   first prime greater than 11 is 13
   enter n > 1 (c-d to exit): ^d
   exiting . .
   

6. Write a pseudocode algorithm to meet this I/O spec:

   enter n > 1 (c-d to exit): 2
   first 2 primes: 2  3
   enter n > 1 (c-d to exit): 5
   first 5 primes: 2  3  5  7  11
   enter n > 1 (c-d to exit): ^d
   exiting . .
   

7. Write a pseudocode algorithm to meet this I/O spec:

   enter n > 1 (c-d to exit): 2
   sum of the first 2 primes: 5
   enter n > 1 (c-d to exit): 5
   sum of the first 5 primes: 28
   enter n > 1 (c-d to exit): ^d
   exiting . .
   

8. Example: use Unix I/O redirection to run primeTest:

           % primeTest < prime.in >! prime.out