Prime Numbers and Fibonacci

Try this:

using System;

class Program

{

static void Main()

{

int n ;

while(true)

{

Console.Write("Enter a positive integer or 0 to finish : ");

int.TryParse(Console.ReadLine(), out n);

if (n == 0) return;

if (n < 0)

{

Console.WriteLine("Negative integers not allowed!");

continue;

}

if(IsPrime(n))

{

Console.WriteLine("{0} is a prime number", n);

}

else

{

Console.WriteLine("{0} is not a prime number", n);

}

if(IsFibonacci(n))

{

Console.WriteLine("{0} is a Fibonacci number", n);

}

else

{

Console.WriteLine("{0} is not a Fibonacci number", n);

}

Console.WriteLine();

}

static bool IsPrime(int x)

{

if (x <= 1) return false;

for (int i = 2; i <= x / 2; i++)

{

if ((x % i) == 0)

{

return false;

}

return true;

}

static bool IsFibonacci(int x)

{

if (x == 1 ) return true;

int first = 1;

int second = 1;

int third = 2;

while(third <= x)

{

if (third == x) return true;

first = second;

second = third;

third = first + second;

}

return false;

}

1 Reply

Know the answer? Post it — somebody with the same question will find it here.

Vulpes11y ago
Try this:

using System;

class Program
{
static void Main()
{
int n ;

while(true)
{
Console.Write("Enter a positive integer or 0 to finish : ");
int.TryParse(Console.ReadLine(), out n);
if (n == 0) return;

if (n < 0)
{
Console.WriteLine("Negative integers not allowed!");
continue;
}

if(IsPrime(n))
{
Console.WriteLine("{0} is a prime number", n);
}
else
{
Console.WriteLine("{0} is not a prime number", n);
}

if(IsFibonacci(n))
{
Console.WriteLine("{0} is a Fibonacci number", n);
}
else
{
Console.WriteLine("{0} is not a Fibonacci number", n);
}

Console.WriteLine();
}
}

static bool IsPrime(int x)
{
if (x <= 1) return false;

for (int i = 2; i <= x / 2; i++)
{
if ((x % i) == 0)
{
return false;
}
}

return true;
}

static bool IsFibonacci(int x)
{
if (x == 1 ) return true;
int first = 1;
int second = 1;
int third = 2;

while(third <= x)
{
if (third == x) return true;
first = second;
second = third;
third = first + second;
}

return false;
}
}
+1