Find remainder without using modulo or % operator

Given two numbers ‘num’ and ‘divisor’, find remainder when ‘num’ is divided by ‘divisor’.
The use of modulo or % operator is not allowed.

Examples :

Input:  num = 100, divisor = 7
Output: 2

Input:  num = 30, divisor = 9
Output: 3

The idea is simple, we run a loop to find the largest multiple of ‘divisor’ that is smaller than or equal to ‘num’.
Once we find such a multiple, we subtract the multiple from ‘num’ to find the divisor.


// C++ program to find remainder without using modulo operator 
#include <iostream> 
using namespace std; 
  
// This function returns remainder of num/divisor without  
// using % (modulo) operator 
int getRemainder(int num, int divisor) 
{ 
    // Handle divisor equals to 0 case 
    if (divisor == 0) 
    { 
        cout << "Error: divisor can't be zero \n"; 
        return -1; 
    } 
  
    // Handle negative values 
    if (divisor < 0) divisor = -divisor; 
    if (num < 0)     num = -num; 
  
    // Find the largest product of 'divisor' that is smaller  
    // than or equal to 'num' 
    int i = 1; 
    int product = 0; 
    while (product <= num) 
    { 
        product = divisor * i; 
        i++; 
    } 
  
    // return remainder 
    return num - (product - divisor); 
} 
  
// Driver program to test above functions 
int main() 
{ 
 //   cout << 100 %0; 
    cout << getRemainder(100, 7); 
    return 0; 
}