﻿ C++ : Check whether a given number is palindrome or not

# C++ Exercises: Check whether a given number is palindrome or not

## C++ Numbers: Exercise-38 with Solution

Write a program in C++ to check whether a given number is palindrome or not.

Sample Solution:

C++ Code :

``````#include <iostream>
using namespace std;
int main()
{
int i,n1,r,s=0;
cout << "\n\n Check whether a given number is palindrome or not: \n";
cout << " -------------------------------------------------------\n";
cout << " Input a number: ";
cin>>n1;
for(i=n1;i>0; )
{
r=i % 10;
s=s*10+r;
i=i/10;
}
if(s==n1)
{
cout<<" "<<n1<<" is a Palindrome Number."<<endl;
}
else
{
cout<<" "<<n1<<" is a not Palindrome Number."<<endl;
}
}
``````

Sample Output:

```Check whether a given number is palindrome or not:
-------------------------------------------------------
Input a number: 141
141 is a Palindrome Number.
```

Flowchart:

C++ Code Editor:

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## C++ Programming: Tips of the Day

How to use the PI constant in C++?

On some (especially older) platforms (see the comments below) you might need to

#define _USE_MATH_DEFINES and then include the necessary header file:
`#include<math.h>`

and the value of pi can be accessed via:

`M_PI`

In math.h (2014) it is defined as:

`# define M_PI           3.14159265358979323846  /* pi */`

but check your math.h for more. An extract from the "old" math.h (in 2009):

```/* Define _USE_MATH_DEFINES before including math.h to expose these macro
* definitions for common math constants.  These are placed under an #ifdef
* since these commonly-defined names are not part of the C/C++ standards.
*/```

However:

1. on newer platforms (at least on my 64 bit Ubuntu 14.04) I do not need to define the _USE_MATH_DEFINES
2. On (recent) Linux platforms there are long double values too provided as a GNU Extension:
`# define M_PIl          3.14159265358979323846`

Ref: https://bit.ly/3G4BgzQ