Prime divisors of a number in C++ [closed] - c++

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Closed 9 years ago.
This is my first question on Stackoverflow, so please excuse me if I'm doing something wrong. :) Can you help me with this code? Thank you! :)
#include <iostream>
using namespace std;
1)
int divisor(int a) // function that checks the divisors of a number *)
{
int i=1; // counter
while(i<=a) // while the counter is less than the number given
{
int i;
if(primes(i)) // here i get the error "primes was not declared in this scope
{
if(a%i==0) // if the remainder of the operation is 0, the number is a divisor
{
cout<<"The divisors of the number are: "<<i<<endl; // prints the divisors
++i; // counter is incremented
}
}
else // else it is not, and the counter i is incremented
{
++i;
}
}
}
2)
int primes(int number) // checks if a number is prime
{
int i;
for(i=2;i<number;i++) // for loop until the counter i is less than a number
{
if(number%i==0) // if the remainder of the operation is 0, the number is not prime
{
break;
}
else //else the number is prime
cout<<number;
break;
}
}
}
3)
int main()
{
int n,i;
cout<<"Give the number: ";
cin>>n;
for(i=2;i<n;i++)
{
divisor(n);
}
}

Answer 1

There are several issues:
1) You need to forward-declare primes() before divisors():
int primes(int number);
2) Your primes() function fails to return a value.
3) Not all code paths in divisor() increment i.
I am sure there are more problems, but this should get you started...

Answer 2

Assuming that the order you give above is the same order as you use in the file, the problem is that your divisor function comes first and makes use of the primes function which is declared later. The easiest (and I guess also most common) solution is to use "foward-delcaration". This means that at the top of your file you state:
int divisor(int);
int primes(int);
In addition you are forgetting to have primes() return a value. (As this question is tagged as
C++, you might even consider having it return a bool instead of an int).
Also in primes the else clause will now cause a break, but I don't think that's altogether wise. Numbers like 9 will end up in that clause when dividing by 2, but the fact that it is not divisible by 2, doesn't make it prime...
There are also other "smart tricks" when it comes to finding primes, but perhaps that is out of the scope of this question.