int in function vs int before function

Question

Need some help knowing what I'm doing wrong. I was doing the palindrome question on C++ and here is the code i was using that always output that it was not a palindrome:

#include <iostream>
using namespace std;

bool isPalindrome(int x) {
//complete the function
int newx, reversex, remainder;
newx = x;
while (newx!=0) {
remainder = newx%10;
reversex = reversex*10 + remainder;
newx /= 10;
}
if (x==reversex) {
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;
}

All i had to do in order to make the code work correctly was declare int reversex before the bool function, like this:

#include <iostream>
using namespace std;

int reversex;
bool isPalindrome(int x) {
//complete the function
int newx, remainder;
newx = x;
while (newx!=0) {
remainder = newx%10;
reversex = reversex*10 + remainder;
newx /= 10;
}
if (x==reversex) {
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;
}

Can anyone tell me why this is?? Thanks in advance.

Answer 1

Christopher Blankenship
In your first code , reversex is containing garbage value by default.
Initialize it to 0 first then code will work fine.

In your second code, reversex is a global variable. By default Global variables are automatically initialized to 0 at the time of declaration. That is why it is already working fine.

reference:
https://www.tutorialspoint.com/why-are-global-and-static-variables-initialized-to-their-default-values-in-c-cplusplus

Answer 2

Christopher Blankenship

You are using temporary variable newx in while loop, instead you should use x like

while (x != 0) {
reminder = x % 10;
reversex = reversex * 10 + reminder;
x /= 10;
}

Now compare temporary variable newx with reversex

if (newx == reversex)
return true;
else
return false;

or you can directly return like this:

return (newx == reversex);

------------xxxx-------

bool isPalindrome(int x) {
//complete the function
int newx, reversex;
newx = x;

while (x != 0) {

reversex = reversex * 10 + x % 10;
x /= 10;
}

return (newx == reversex);

}