Printing all palindrome numbers in a given range - c++

Question

I'm trying to write a program that would print all palindrome in range [a, b]. I've written this so far, but nothing is printed after I input the values for a, b. What is missing?
#include "stdafx.h"
#include <iostream>
using namespace std;
int t = 0, rmd, z, a, b;
int reverse() {
while (z != 0) {
rmd = z% 10;
t = t * 10 + rmd;
z/= 10;
}
return t;
}
int palin() {
if (a == reverse()) {
return 1;
}
else
return 0;
}
int main() {
cout << "a: "; cin >> a;
cout << "b: "; cin >> b;
while (a <= b) {
z = a;
if (palin())
cout << a << endl;
a++;
}
system("pause");
return 0;
}

Answer 1

The problem is that the variable t is not local to your reverse() function. Its value survives to the following invocation, so the result of reverse becomes junk unrelated to the actual call.
You need to make t local to reverse() in order to fix this problem.
In general, it is a good idea to develop a habit of declaring your variables in the innermost scope to which they could belong without breaking your code. In this case, this would be the scope of reverse() function for t, and the scope of main for the remaining variables; palin should take a as its parameter.

Answer 2

Your use of variables is what is confusing you. The actual issue is not setting t to zero every time you call reverse, but you should think about how you use variable scoping and what functions actually do. Right now you have 2 procedures, that perform actions on global data. Instead try to formulate the problem using functions that accept arguments, and return a result.
#include <iostream>
using namespace std;
int reverse(int z) {
int t = 0;
int rmd;
while (z != 0) {
rmd = z % 10;
t = t * 10 + rmd;
z/= 10;
}
return t;
}
int palin(int z) {
return z == reverse(z);
}
int main() {
int a, b;
cout << "a: "; cin >> a;
cout << "b: "; cin >> b;
while (a <= b) {
if (palin(a)) {
cout << a << endl;
}
a++;
}
system("pause");
return 0;
}