Thread: Prime factors of an integer and sorting them in descending order.

Code:

#include<iostream>
#include<stack>
using namespace std;
void PrimeFactors(int n)
{
  // Stores prime factors of n
  // in decreasing order
  stack < int >x;
  int i = 2;
  while (n != 1) {

    if (n % i == 0) {

      // Insert i into stack
      x.push(i);

      while (n % i == 0) {

        // Update n
        n = n / i;
      }
    }
    // Update i
    i++;
  }

  // Print value of stack x
  while (!x.empty()) {

    printf("%d ", x.top());
    x.pop();
  }
}

// Driver Code
int main()
{
  int n;
  cout << "Enter value:";
  cin >> n;
  // function Call
  PrimeFactors(n);
  return 0;
}

insert

Code:

Output:
Enter value:76 19 2 
im supposed to see 
19 2 2

1. When posting on forums (or indeed anywhere), it's a good idea to use "copy as text" in your IDE and/or "paste as text" in your browser. If the thing you're copying to doesn't understand the fancy markup added by your IDE, then the result is a mess.

2. Your code only inputs one value, yet you claim to type in three?

3. If the code doesn't work, try adding some debug prints, like so.

Code:

  while (n != 1) {
    cout << "DEBUG: Loop: " << n << " " << i << endl; 
    if (n % i == 0) {
      cout << "DEBUG: push: "  << i << endl; 
      // Insert i into stack
      x.push(i);
 
      while (n % i == 0) {
         // Update n
        n = n / i;
      }
      cout << "DEBUG: new n: "  << n << endl; 
    }
    // Update i
    i++;
  }

When you see a DEBUG that doesn't match your expectation of what you think should have happened, you've found a bug.

Whether that bug is in your code, or your understanding of the problem is something for you to figure out.

Code:

Code:

#include <stack>
using namespace std;  
void PrimeFactors(int n){
    // Stores prime factors of n
    // in decreasing order
    stack<int> x;
    int i = 2;
    while (n != 1) {
        if (n % i == 0) {
 
            // Insert i into stack
            x.push(i);
 
            while (n % i == 0) {
 
                // Update n
                n = n / i;
            }
        }
 
        // Update i
        i++;
    }
 
    // Print value of stack x
    while (!x.empty()) {
 
        printf("%d ", x.top());
        x.pop();
    }
}
// Driver Code
int main(){
    int n;
    cout <<"Enter value:";
    cin >> n;
    // function Call
    PrimeFactors(n);
    return 0;
}

ive tried the debug and here is the output:
Enter value:76
DEBUG: Loop: 76 2
DEBUG: push: 2
DEBUG: new n: 19
DEBUG: Loop: 19 3
DEBUG: Loop: 19 4
DEBUG: Loop: 19 5
DEBUG: Loop: 19 6
DEBUG: Loop: 19 7
DEBUG: Loop: 19 8
DEBUG: Loop: 19 9
DEBUG: Loop: 19 10
DEBUG: Loop: 19 11
DEBUG: Loop: 19 12
DEBUG: Loop: 19 13
DEBUG: Loop: 19 14
DEBUG: Loop: 19 15
DEBUG: Loop: 19 16
DEBUG: Loop: 19 17
DEBUG: Loop: 19 18
DEBUG: Loop: 19 19
DEBUG: push: 19
DEBUG: new n: 1

my expected output is 19 2 2

> ive tried the debug and here is the output:
So what did you learn from it?

You went from 76 down to 19 (presumably via 38), but you only have one '2' pushed onto your stack.

Maybe you need to be pushing additional results?