﻿ C++ Exercises: Generate random integers in a specific range - w3resource

# C++ Exercises: Generate random integers in a specific range

## C++ Numbers: Exercise-8 with Solution

Write a program in C++ to generate random integers in a specific range.

Pictorial Presentation:

Sample Solution:

C++ Code :

``````#include <cstdlib>
#include <ctime>
#include <iostream>

using namespace std;

int main()
{
int ln,un;
cout << "\n\n Generate random integer in a specific range: \n";
cout << " --------------------------------------------------\n";
cout << " Input the lower range of number: ";
cin >> ln;
cout << " Input the upper range of number: ";
cin >> un;
srand(time(NULL));
cout<<" The random number between "<<ln<<" and "<<un<<" is: ";
cout <<  ln+rand() % static_cast<int>(un-ln+1) << endl;
return 0;

}
``````

Sample Output:

```Generate random integer in a specific range:
--------------------------------------------------
Input the lower range of number: 15
Input the upper range of number: 25
The random number between 15 and 25 is: 18
```

Flowchart:

C++ Code Editor:

What is the difficulty level of this exercise?

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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