Find prime factors of a number – Computer Sir Ki Class


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Find prime factors of a number

Finding prime factors of a number input by the user.

Learning Objectives

  • Finding factors of number up to a level where all factors are prime.

Source Code

TC++ #3218


Source Code

Run Output

Enter a positive integer: 1224
The prime factors are: 2 2 2 3 3 17

Code Understanding

int n; cout<<“Enter a positive integer: “; cin>>n;
Collecting the input number from the user.

cout<<“The prime factors are: “; //Prompt before printing
for (int i=2; i <= n; i++) //Begins from 2 as no prime factor can not be less than 2
while(n % i == 0) //This loop works till the factor is identified
n /= i;                  //When identified the number is reduced by dividing with identified number
cout<<i<<” “; //Identified number is printed.


  • This code can be modified slightly to get prime factor only once.
  • One can also modified it to store prime-factor in an array and then manipulate the array as required.
  • Every positive integer number can be reduced to its prime factors because after reducing to prime factor further factorisation would not be possible, as a prime number is divisible by 1 and the number itself.

Suggested Filename(s): primefac.cpp


sunmitra| Created: 31-Jan-2018 | Updated: 15-Sep-2018|

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