﻿ C++ Exercises: List non-prime numbers from 1 to an upperbound - w3resource

# C++ Exercises: List non-prime numbers from 1 to an upperbound

## C++ For Loop: Exercise-16 with Solution

Write a C++ program to list non-prime numbers from 1 to an upperbound.

Visual Presentation:

Sample Solution :-

C++ Code :

``````#include <iostream> // Include input-output stream header
#include <cmath>    // Include math functions header

using namespace std; // Using standard namespace to avoid writing std::

int main() // Start of the main function
{
int ult; // Declaration of variable 'ult' to store the upper limit
cout << "\n\n List non-prime numbers from 1 to an upperbound:\n"; // Display message on the console
cout << "----------------------------------------------------\n";
cout << " Input the upperlimit: "; // Prompt the user to input the upper limit
cin >> ult; // Read the input value as the upper limit

cout << " The non-prime numbers are: " << endl; // Display message for non-prime numbers

// Loop through numbers from 2 to the upper limit to check for non-prime numbers
for (int num = 2; num <= ult; ++num)
{
int mfactor = (int)sqrt(num); // Find the square root of the number and cast it to an integer as the maximum factor to check

// Loop to check for factors of the current number from 2 to its square root
for (int fact = 2; fact <= mfactor; ++fact)
{
// If the current number is divisible by 'fact', it's not a prime number
if (num % fact == 0)
{
cout << num << " "; // Display the non-prime number
break; // Break the loop to move to the next number
}
}
}
cout << endl; // Output a newline
return 0; // Indicates successful termination of the program
}
``````

Sample Output:

``` List non-prime numbers from 1 to an upperbound:
----------------------------------------------------
Input the upperlimit: 25
The non-prime numbers are:
4 6 8 9 10 12 14 15 16 18 20 21 22 24 25
```

Flowchart:

C++ Code Editor: