Find all palindrome numbers within a given range using a check function

Question

I am trying to find all the palindrome numbers under a given limit number using a check function.

This is my code:

#include<iostream>
using namespace std;

int checkPalindrom(int);
int main(){
    int num,sum;
    int lim;

    cout << "Insert limit number: ";
    cin >>  lim;

    cout << "Palindrome numbers within the limit are: ";
    for(num>0;num<=lim;num++){
        sum=checkPalindrom(num);
        if(num==sum)
            cout << num << " ";
    }
    return 0;
}

int checkPalindrom(int num){
    int sum=0,r;
    if (num){
        r=num%10;
        sum=sum*10+r;
        checkPalindrom(num/10);
    }
    return sum;
}

The result here is palindrome numbers till 9, despite 2 digits < number

Thank you in advance for your answers!

Answer 1

Change this

for(num>0;num<=lim;num++)

to this

for(num=0;num<=lim;num++)

in order to initialize num.

then actually you need to make more changes. This should work:

#include<iostream>
using namespace std;

bool checkPalindrom(int);
int main() {
  int num;
  int lim;

  cout << "Insert limit number: ";
  cin >> lim;

  cout << "Palindrome numbers within the limit are: ";
  for (num = 0; num <= lim; num++) {
    if (checkPalindrom(num))
      cout << num << " ";
  }
  return 0;
}

bool checkPalindrom(int num) {
  int n = num;
  int dig, rev = 0;
  while (num > 0) {
    dig = num % 10;
    rev = rev * 10 + dig;
    num  /= 10;
  }
  return (n == rev);
}

The solution is based in this answer.

The main problem with your code, was that you were not even using a loop, but an if statement inside your function.