Why does the first one work and the second doesn't?

Question

#include <iostream>
using namespace std;
int main() {
int n,num,rev=0,digit;
cin>>num;
n=num;
do
{
digit=num%10;
rev=(rev*10)+digit;
num/=10;
}while(num!=0);

if (n==rev){
cout<<n<<" is a palindrome";
}
else{
cout<<n<<" is not a palindrome";
}

return 0;
}
This one work just fine

#include <iostream>
using namespace std;
int main() {
int num,rev=0,digit;
cin>>num;
while(num!=0){
digit=num%10;
rev=(rev*10)+digit;
num/=10;
}

if (num==rev){
cout<<num<<" is a palindrome";
}
else{
cout<<num<<" is not a palindrome";
}

return 0;
}
This one keeps giving me 0 as a value, and I have no Idea why.

Answer 1

In first snippet, you copied <num> into <n> before running the loop. You compare <n> to <rev> afterwards. This is fine as <n> contains the original value of <num>.

In second snippet, you went on with the loop, which stops when <num> becomes zero. You didn't have a copy of the original input.

Answer 2

Rakin in the second one you're printing the value of num and not n, n does not exist, store a copy of the original input

Answer 3

#include <iostream>
using namespace std;
int main() {
int num,n,rev=0,digit;
cin>>num;
n=num;
while(num!=0){
digit=num%10;
rev=(rev*10)+digit;
num/=10;
}

if (n==rev){
cout<<n<<" is a palindrome";
}
else{
cout<<n<<" is not a palindrome";
}

return 0;
}

Answer 4

Oh Ok I got it now. Thanks to everyone who replied. I see what I did wrong

Answer 5

the num variable is 0