Appropriate usage of functions

This is a discussion on Appropriate usage of functions within the C++ Programming forums, part of the General Programming Boards category; Hi everyone, I have just finished the practice problem 3 from chapter 7 and I have commented it in at ...

  1. #1
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    Appropriate usage of functions

    Hi everyone,

    I have just finished the practice problem 3 from chapter 7 and I have commented it in at the top. I did this so I could quickly look at what the problem was without switching back over to pdf. This is it:

    Code:
    /*
     Design a program that finds all numbers from 1 to 1000 whose prime factors, when added
     together, sum up to a prime number (for example, 12 has prime factors of 2, 2, and 3, which sum to 7, which is prime). Implement the code for that algorithm.
    */
    
    #include <iostream>
    #include <cmath>
    
    int getSumOfPrimeFactors(int number);
    bool sumOfPrimeFactorsIsPrime(int number);
    
    int main()
    {
        for (int i = 1; i <= 1000; i++)
        {
            if (sumOfPrimeFactorsIsPrime(getSumOfPrimeFactors(i)))
    /*
    BREAKS DOWN LIKE THIS (FOR MY SELF REFERENCE!):
    if (sumOfPrimeFactorsIsPrime(getSumOfPrimeFactors(i))) - i is substituted with loop variable, 1 through 1000
    --- if (sumOfPrimeFactorsIsPrime(getSumOfPrimeFactors(12))) - sum of prime factors for 12 are 2 x 2 x 3, so added, 2 + 2 + 3 = 7
    ------ if (sumOfPrimeFactorsIsPrime(7)) - function works out whether 7 is a prime number or not, returns true or false
    --------- if (true)
    ------------print number
    */
            {
                std::cout << i << " has prime factors that add together to equal a prime number!" << std::endl;
                std::cout << "The sum of the prime factors are: " << getSumOfPrimeFactors(i) << std::endl << std::endl;
            }
        }
    }
    
    
    int getSumOfPrimeFactors(int number) //gets the prime factors of the number (using variable x)
    {    
        int x = 2;
        int sumOfPrimeFactors = 0;
        
        while (x <= number)
        {
            if (number % x == 0)
            {
                number = number / x;
                sumOfPrimeFactors = sumOfPrimeFactors + x; //adds together the prime factors of the number
            }
            else
            {
                x++;
            }
        }
        
        return sumOfPrimeFactors; //returns the value of the prime factors added together to be used in function sumOfPrimeFactorsIsPrime(int number)
    }
    
    bool sumOfPrimeFactorsIsPrime(int number) //works out if a number is prime or not, returns true or false accordingly
    {
        //divide each test number from isPrime(i) by up-to-or-equal the square root to find prime
        for ( int i = 2; i <= sqrt(number); i++)
        {
            if (number % i == 0)
            {
                return false;
            }
        }
        return true;
    }
    First I have to find the prime factors, then add them up, then test whether the resulting number is a prime or not. I couldn't think of another way of doing this without nesting some functions together as they all rely on each other, like a chain.

    It seems to work ok, but my question is whether this is the sort of thing you would be expected to do with functions in a problem like this (if that makes sense).

    1) Should more be in 'int main()' rather than all dumped into functions?
    2) Is nesting functions a standard thing to do in cases like this?

    Any advice on how I can improve on things are always welcome. Thanks.

    p.s. I apologise for the poor thread title, couldn't think on how to describe this exactly.

  2. #2
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    That's what functions are supposed to do. Usually to shorten the code or make things look more clear without having to dump the whole code in main. I didn't test it, but they seem fine.

  3. #3
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    Ok, thanks.

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