How did this give me the sum of the numbers?

[Tej Samra]

I earlier posted a topic to help me do this but i didnt have a code. I have finally completed this with a help of a local friend but i dont understand the logic of it.

#include <cstdlib>
#include <iostream>

using namespace std;

int main()
{
  int number;
  int sum=0;
  
  cout << "Enter an integer:";
  cin >> number;
  
  while(number>0){
  sum=sum+number%10; // sum + 2.1%10 is supposedly the output which is 3? How so
  number=number/10; // number=21/10 which is 2.1
}
  cout << "The sum is" << sum << endl;
    
    system("PAUSE");
    return (0);
}

when I run the code if I input integer for example 21 it will give me 3 as a sum which is correct.

I dont understand how the sum will be 3 if its (0=sum+2.1%10) because 2.1%10 doesnt equal to 3 or does it??

[firedraco]

number=number/10; // number=21/10 which is 2.1

This actually won't be 2.1. Since you have two integers (number and 10), you are doing integer division so the result is truncated, and you get 2.

[Tej Samra]

oh I see but then how is the sum 3? if the result is 2 it is (sum=sum+2%10)

which i just tested and 2%10 is 2 so (sum=0+2) which (sum=2) but then how is it equal to 3

[firedraco]

Number starts at 21 so the first time through the loop you have:

sum += num % 10; //sum += 2
number /= 10; //num is now 1

Next loop, num is > than 1 so you are ok

...