Can Someone Please Explain the Palindrome Code Coach?

Question

I was having trouble solving the palindrome code coach and ended up having to search for help on how to solve it. I was trying to use a for loop to reverse the numbers but then couldn't figure out how to return the variable back to main to determine if it was true or false. I was only getting half of the problem correct. I found this solution on the discussions and was trying to interpret it, but I don't understand what is happening after the first function is called. Can someone please break down each section as to what is happening so I can better understand this? Thank you in advance!

#include <iostream>
using namespace std;

int revDigit(int y)
{
int rem, rev = 0;
while(y>0)
{
rem = y % 10;
rev = rev * 10 + rem;
y /= 10;
}return rev;
}

bool isPalindrome(int x) {
if(x == revDigit(x))
{
return true;
}
else
{
return false;
}

}

int main() {
int n;
cin >>n;

if(isPalindrome(n)) {
cout <<n<<" is a palindrome";
}
else {
cout << n<<" is NOT a palindrome";
}
return 0;
}

Answer 1

palindrome checks if two numbers are the same if they are reversed.

isPalindrome function checks if x number is the same as revDigit, which outputs the reverse of the digit.

how revDigit works is by taking the mod of 10 from y which is the rightmost number to rem.

so if y = 456
rem = y % 10 // rem value will be 6

then rev would multiply by 10 to give space to the rightmost number and add rev

so rev would first be
rev = 6
rev = 60 + 5 = 65
rev = 650 + 4 = 654

keep looping and make y divide by 10 to remove the rightmost number until y turns 0.
and you get rev which is the reverse number.

Answer 2

Is it failing any test cases?

edit:

@Trevor Biroschik

* first taking input
* it is calling isPolindrome(n) on input, which returns true or false about Palindrome correctness, by checking input x to value returned from
* another function revDigits(x) which returns a reversed value of input , within the function
ex: 234 to 432
ex2: 232 to 232
first example returns false and next returns true...

edit:

It would be better to tell, which specific lines of code you are not understanding...

hope it clears..

Answer 3

G'day Trevor Biroschik did you understand the rev=rev*10 +(y%10) part?

To send the result of the function back, you use "return (variable_name)" in this case it is
👉return rev👈 .

To ask for that return, the isPalindrome function has the line
👉if(x == revDigit(x))👈
so the return of revDigit will be inserted in to that line. It works out to be

if(x == (the return value from the revDigit function)

Does that explain "return" ok?

Answer 4

@Shen thank you so much! That makes sense to me now.

@Jayakrishna your explanation was well said piece by piece and I thank you for that. Pretty much I wanted to understand when the revDigit(x) function was called. But I understand now that it's being called while also being compared to x.

@Hungry that does explain the return, thank you so much!