Can someone explain to me the logic behind this output

Question

Following is the code I've had in a quiz recently and I tried but am unable to understand logic behind the answer for the Output..

#include <iostream>
using namespace std;

int main() {
int x=3;

switch(3){
case 1: {x+=x;}
case 3: {x+=x;}
case 5: {x+=x;}

default : {x+=5;}
}
cout <<x;
return 0;

OUTPUT: 17

Answer 1

You're not using break statements so cases 3, 5 and default are executed.

x = 3
case 3: x+=x // x = 6
case 5: x+=x // x = 12
default: x+=5 // x = 17

Answer 2

Anna Omg I totally missed that.. Thankyou soo much