Large number mod

large_num.cpp

// Function to compute num (mod a) 
int mod(string num, int a) 
{ 
    // Initialize result 
    int res = 0; 
  
    // One by one process all digits of 'num' 
    for (int i = 0; i < num.length(); i++) 
         res = (res*10 + (int)num[i] - '0') %a; 
  
    return res; 
}