what is the problem of this code and why this code always run the "non-palindrome" even though i checked algorithm several times

Question

#include <iostream>
bool isPalindrome(int x){
int a,sum=0;

while(x>0){
a=x%10;
sum=sum*10+a;
x=x/10;

}

}

int main()

{
int x;
int sum;
std::cin>>x;
if(isPalindrome(x))

{std::cout<<sum<<"is a palindrome";}

else

{std::cout<<sum<<"is not a palindrome";}

}

Answer 1

Possible problems are:

1) isPalindrome() returns no boolean,
2) it doesn't determine whether x is palindrome or not.

Cheer!

Answer 2

Hi Martin Taylor
I agree that a string problem is easier to resolve, but I find this approach quite interesting.

Answer 3

You haven't compared your input value and sum ......and then u haven't returned any Boolean value too...
This code will do...

#include <iostream>
bool isPalindrome(int p){
int a,sum=0,c=p;

while(c>0){
a=c%10;
sum=sum*10+a;
c=c/10;

}
if(p==sum)
return true;
else
return false;

}

int main()

{
int x;

std::cin>>x;
if(isPalindrome(x))

{std::cout<<x<<" is a palindrome";}

else

{std::cout<<x<<" is not a palindrome";}

}

Answer 4

Yep, his code is very close. I hope he make it his way……

Answer 5

Rik Wittkopp i have run the adjusted version which you recommend but the problem is why rhe out put is always non palindrom and doesnt give a right conditional , for example when you enter 252 it says it is non palindrome and its wrong.

Answer 6

#include <iostream>
bool isPalindrome(int x){
int a,sum=0;

while(x>0){
a=x%10;
sum=sum*10+a;
x=x/10;

}
return sum;

if (sum==x)
return true;
else
return false;

}
int main()

{
int x;
//int sum;
std::cout<<isPalindrome(887);
std::cin>>x;
if(isPalindrome(x))

{std::cout<<x<<"is a palindrome";}

else

{std::cout<<x<<"is not a palindrome";}

}

But why now it returns always true and the conditionals doesnt work as it should?

Rik Wittkopp
Shizuku
Martin Taylor

Answer 7

You have an excess return statement.
It returns always true and quits the program before if-else statement.

Note that any non-zero value will be considered true!

Answer 8

But Shizuku is there a way to give the problem a function which qould have have the right boolean form?
You know how would i write this section?

Answer 9

Just ONE malicious line, bro.

And mind you, inside main() should not have been altered.

Maybe original main() goes like:

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

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

Good luck.

Answer 10

Nariman Tajari
I know that you have received a number of solutions already, but I would like to present a working solution using the concepts of our discussion.

#include <iostream>
bool isPalindrome(int num){
int a,x,sum=0;
x = num;

while(x>0){
a=x%10;
sum=sum*10+a;
x=x/10;
}
return sum == num;
}

int main(){
int x;
std::cin>>x;

if(isPalindrome(x)){
std::cout<<x<<" is a palindrome";
}
else {
std::cout<<x<<" is not a palindrome";
}
}

Answer 11

Nariman Tajari
There are a number of problems with your code.

1. Your Boolean function does not work.
It did not have a return from the function so no result could be produced when the function was called.
Also, your variable sum =0, but later you want a value multiplied by sum, which will be 0, 6*0=0.
There is another problem within your logic but I am hoping you can resolve that yourself, (meaning I stopped looking for it)

2. in main() you have int sum.
You then attempt to get a boolean value from your function, followed by a statement referring to sum, which has not yet been assigned to a value.

I have modified your code a bit.
Fix the logic within your bool function & it should work

Delete the test boolean section when ready

Answer 12

Nariman Tajari
The adjusted code I mentioned.

#include <iostream>
bool isPalindrome(int x){
int a,sum=0;

while(x>0){
a=x%10;
sum=sum*10+a;
x=x/10;
}
return sum == x;
}

int main(){

// testing boolean function
std::cout << isPalindrome(262)<<std::endl;

int x;
//int sum;
std::cin>>x;

if(isPalindrome(x)){
std::cout<<x<<" is a palindrome";
}
else {
std::cout<<x<<" is not a palindrome";
}
}

Answer 13

Nariman Tajari
I fixed your bool function, which I will attach.
I have left all my test notes in place for you to review.

The problem was that x was being reduced to 0, while sum was being constructed

#include <iostream>
bool isPalindrome(int num){
int a,x,sum=0;
x = num;
std::cout<<x << std::endl;

while(x>0){
a=x%10;
sum=sum*10+a;
x=x/10;
//std::cout << a << std::endl;
std::cout << sum << std::endl;
}
std::cout << x << std::endl;
return sum == num;
}

int main(){

// testing boolean function
std::cout << isPalindrome(262)<<std::endl;

}

Answer 14

#include <algorithm>
#include <string>
#include <cmath>
#include <vector>
#include <iostream>

int lengthValue(int );
bool isPalindrome(int );
int main( ){
std::cout<<std::boolalpha<<isPalindrome(555);
return 0;
}

int lengthValue( int value){
int i=0;
while ( value > 0){
value /= 10;
++i;
}
return i;
}

bool isPalindrome(int value){
int length=lengthValue(value);
std::vector<int> vec, vec2;
int i(0);
int divide;
for (int i=length-1; i >=0 ; --i){
divide = value / (int)std::pow(10,i);
value %= (int) std::pow(10,i);
vec.push_back(divide);
}

vec2 = vec;
std::reverse(vec2.begin(),vec2.end());

if ( vec == vec2)
return true;
return false;
}