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Count Even and Odd numbers in a range

Counting even and odd numbers in a range involves determining the number of integers within a specified range that are either even or odd. An even number is a number that is divisible by 2 without leaving any remainder, while an odd number is a number that is not divisible by 2 without leaving a remainder.

To count even and odd numbers in a range, you can iterate over all the integers in the range and check whether each integer is even or odd. If the integer is even, increment a counter for even numbers. Similarly, if the integer is odd, increment a counter for odd numbers.

Here's an example code snippet in Python that counts even and odd numbers in a range from 1 to 10:

start = 1
end = 10
even_count = 0
odd_count = 0

for num in range(start, end+1):
    if num % 2 == 0:
        even_count += 1
    else:
        odd_count += 1

print("Number of even numbers:", even_count)
print("Number of odd numbers:", odd_count)

This code outputs:

Number of even numbers: 5
Number of odd numbers: 5

Better solution

To count even and odd numbers in a range without using loop or recursion, you can use the following formula:

  • Count of even numbers = (range_end // 2) - (range_start - 1) // 2
  • Count of odd numbers = (range_end - range_start + 1) - count of even numbers

Here, the "//" operator is used for integer division.

Explanation: To count the number of even numbers in the range, we can divide the range into two halves: the first half contains all even numbers and the second half contains all odd numbers. The number of even numbers in a range can be calculated by counting the number of integers in the first half.

The first half of the range starts at the first even number, which is the smallest even number greater than or equal to the range start. To find the first even number, we can divide the range start by 2 and round up to the nearest integer (using integer division). Similarly, the second half of the range starts at the first odd number, which is the smallest odd number greater than or equal to the range start. To find the first odd number, we can add 1 to the first even number.

Similarly, to count the number of odd numbers in the range, we can subtract the count of even numbers from the total number of integers in the range.

Note that this formula works only for non-negative integers. If the range includes negative integers, the formula needs to be modified accordingly.

Code Solution

We can also calculate the even and odd number efficiently using new approach.

// C program
// Count Even and Odd numbers in a range
#include <stdio.h>

//Count the number of Even and Odd elements in given range
void count_even_odd(int first, int last)
{
	if (first > last)
	{
		//Transform into a valid range
		count_even_odd(last, first);
	}
	else
	{
		int even = 0;
		int odd = 0;
		//Count number of element
		int length = (last - first) + 1;
		if (first % 2 == 0)
		{
			if (last % 2 == 0)
			{
				//When both given number is even
				even = (length / 2) + 1;
			}
			else
			{
				even = length / 2;
			}
			odd = length - even;
		}
		else
		{
			if (last % 2 != 0)
			{
				odd = (length / 2) + 1;
			}
			else
			{
				odd = length / 2;
			}
			even = length - odd;
		}
		printf("\n Range [%d,%d] : Even [%d], Odd [%d] ", first, last, even,odd);
	}
}
int main()
{
	//Test case
	count_even_odd(2, 8);
	count_even_odd(1, 10);
	count_even_odd(21, 33);
	count_even_odd(7, 29);
	count_even_odd(0, 0);
	return 0;
}

Output

 Range [2,8] : Even [4], Odd [3]
 Range [1,10] : Even [5], Odd [5]
 Range [21,33] : Even [6], Odd [7]
 Range [7,29] : Even [11], Odd [12]
 Range [0,0] : Even [1], Odd [0]
/* 
  Java program 
  Count Even and Odd numbers in a range
*/
class EvenOddNumber
{
	//Count the number of Even and Odd elements in given range
	public void count_even_odd(int first, int last)
	{
		if (first > last)
		{
			//Transform into a valid range
			count_even_odd(last, first);
		}
		else
		{
			int even = 0;
			int odd = 0;
			//Count number of element
			int length = (last - first) + 1;
			if (first % 2 == 0)
			{
				if (last % 2 == 0)
				{
					//When both given number is even
					even = (length / 2) + 1;
				}
				else
				{
					even = length / 2;
				}
				odd = length - even;
			}
			else
			{
				if (last % 2 != 0)
				{
					odd = (length / 2) + 1;
				}
				else
				{
					odd = length / 2;
				}
				even = length - odd;
			}
			System.out.print("\n Range [" + first + "," + last + "] : Even [" + even + "], Odd [" + odd + "] ");
		}
	}
	public static void main(String[] args)
	{
		EvenOddNumber obj = new EvenOddNumber();
		//Test case
		obj.count_even_odd(2, 8);
		obj.count_even_odd(1, 10);
		obj.count_even_odd(21, 33);
		obj.count_even_odd(7, 29);
		obj.count_even_odd(0, 0);
	}
}

Output

 Range [2,8] : Even [4], Odd [3]
 Range [1,10] : Even [5], Odd [5]
 Range [21,33] : Even [6], Odd [7]
 Range [7,29] : Even [11], Odd [12]
 Range [0,0] : Even [1], Odd [0]
//Include header file
#include <iostream>
using namespace std;

/*
  C++ program 
  Count Even and Odd numbers in a range
*/

class EvenOddNumber
{
	public:
		//Count the number of Even and Odd elements in given range
		void count_even_odd(int first, int last)
		{
			if (first > last)
			{
				//Transform into a valid range
				this->count_even_odd(last, first);
			}
			else
			{
				int even = 0;
				int odd = 0;
				//Count number of element
				int length = (last - first) + 1;
				if (first % 2 == 0)
				{
					if (last % 2 == 0)
					{
						//When both given number is even
						even = (length / 2) + 1;
					}
					else
					{
						even = length / 2;
					}
					odd = length - even;
				}
				else
				{
					if (last % 2 != 0)
					{
						odd = (length / 2) + 1;
					}
					else
					{
						odd = length / 2;
					}
					even = length - odd;
				}
				cout << "\n Range [" << first << "," << last << "] : Even [" << even << "], Odd [" << odd << "] ";
			}
		}
};
int main()
{
	EvenOddNumber obj = EvenOddNumber();
	//Test case
	obj.count_even_odd(2, 8);
	obj.count_even_odd(1, 10);
	obj.count_even_odd(21, 33);
	obj.count_even_odd(7, 29);
	obj.count_even_odd(0, 0);
	return 0;
}

Output

 Range [2,8] : Even [4], Odd [3]
 Range [1,10] : Even [5], Odd [5]
 Range [21,33] : Even [6], Odd [7]
 Range [7,29] : Even [11], Odd [12]
 Range [0,0] : Even [1], Odd [0]
//Include namespace system
using System;

/* 
  C# program 
  Count Even and Odd numbers in a range
*/

class EvenOddNumber
{
	//Count the number of Even and Odd elements in given range
	public void count_even_odd(int first, int last)
	{
		if (first > last)
		{
			//Transform into a valid range
			count_even_odd(last, first);
		}
		else
		{
			int even = 0;
			int odd = 0;
			//Count number of element
			int length = (last - first) + 1;
			if (first % 2 == 0)
			{
				if (last % 2 == 0)
				{
					//When both given number is even
					even = (length / 2) + 1;
				}
				else
				{
					even = length / 2;
				}
				odd = length - even;
			}
			else
			{
				if (last % 2 != 0)
				{
					odd = (length / 2) + 1;
				}
				else
				{
					odd = length / 2;
				}
				even = length - odd;
			}
			Console.Write("\n Range [" + first + "," + last + "] : Even [" + even + "], Odd [" + odd + "] ");
		}
	}
	public static void Main(String[] args)
	{
		EvenOddNumber obj = new EvenOddNumber();
		//Test case
		obj.count_even_odd(2, 8);
		obj.count_even_odd(1, 10);
		obj.count_even_odd(21, 33);
		obj.count_even_odd(7, 29);
		obj.count_even_odd(0, 0);
	}
}

Output

 Range [2,8] : Even [4], Odd [3]
 Range [1,10] : Even [5], Odd [5]
 Range [21,33] : Even [6], Odd [7]
 Range [7,29] : Even [11], Odd [12]
 Range [0,0] : Even [1], Odd [0]
<?php
/* 
  Php program 
  Count Even and Odd numbers in a range
*/
class EvenOddNumber
{
	//Count the number of Even and Odd elements in given range
	public	function count_even_odd($first, $last)
	{
		if ($first > $last)
		{
			//Transform into a valid range
			$this->count_even_odd($last, $first);
		}
		else
		{
			$even = 0;
			$odd = 0;
			//Count number of element
			$length = ($last - $first) + 1;
			if ($first % 2 == 0)
			{
				if ($last % 2 == 0)
				{
					//When both given number is even
					$even = (intval($length / 2)) + 1;
				}
				else
				{
					$even = intval($length / 2);
				}
				$odd = $length - $even;
			}
			else
			{
				if ($last % 2 != 0)
				{
					$odd = (intval($length / 2)) + 1;
				}
				else
				{
					$odd = intval($length / 2);
				}
				$even = $length - $odd;
			}
			echo "\n Range [". $first .",". $last ."] : Even [". $even ."], Odd [". $odd ."] ";
		}
	}
}

function main()
{
	$obj = new EvenOddNumber();
	//Test case
	$obj->count_even_odd(2, 8);
	$obj->count_even_odd(1, 10);
	$obj->count_even_odd(21, 33);
	$obj->count_even_odd(7, 29);
	$obj->count_even_odd(0, 0);
}
main();

Output

 Range [2,8] : Even [4], Odd [3]
 Range [1,10] : Even [5], Odd [5]
 Range [21,33] : Even [6], Odd [7]
 Range [7,29] : Even [11], Odd [12]
 Range [0,0] : Even [1], Odd [0]
/* 
  Node Js program 
  Count Even and Odd numbers in a range
*/
class EvenOddNumber
{
	//Count the number of Even and Odd elements in given range
	count_even_odd(first, last)
	{
		if (first > last)
		{
			//Transform into a valid range
			this.count_even_odd(last, first);
		}
		else
		{
			var even = 0;
			var odd = 0;
			//Count number of element
			var length = (last - first) + 1;
			if (first % 2 == 0)
			{
				if (last % 2 == 0)
				{
					//When both given number is even
					even = (parseInt(length / 2)) + 1;
				}
				else
				{
					even = parseInt(length / 2);
				}
				odd = length - even;
			}
			else
			{
				if (last % 2 != 0)
				{
					odd = (parseInt(length / 2)) + 1;
				}
				else
				{
					odd = parseInt(length / 2);
				}
				even = length - odd;
			}
			process.stdout.write("\n Range [" + first + "," + last + "] : Even [" + even + "], Odd [" + odd + "] ");
		}
	}
}

function main()
{
	var obj = new EvenOddNumber();
	//Test case
	obj.count_even_odd(2, 8);
	obj.count_even_odd(1, 10);
	obj.count_even_odd(21, 33);
	obj.count_even_odd(7, 29);
	obj.count_even_odd(0, 0);
}
main();

Output

 Range [2,8] : Even [4], Odd [3]
 Range [1,10] : Even [5], Odd [5]
 Range [21,33] : Even [6], Odd [7]
 Range [7,29] : Even [11], Odd [12]
 Range [0,0] : Even [1], Odd [0]
#   Python 3 program 
#   Count Even and Odd numbers in a range

class EvenOddNumber :
	# Count the number of Even and Odd elements in given range
	def count_even_odd(self, first, last) :
		if (first > last) :
			# Transform into a valid range
			self.count_even_odd(last, first)
		else :
			even = 0
			odd = 0
			# Count number of element
			length = (last - first) + 1
			if (first % 2 == 0) :
				if (last % 2 == 0) :
					# When both given number is even
					even = (int(length / 2)) + 1
				else :
					even = int(length / 2)
				
				odd = length - even
			else :
				if (last % 2 != 0) :
					odd = (int(length / 2)) + 1
				else :
					odd = int(length / 2)
				
				even = length - odd
			
			print("\n Range [", first ,",", last ,"] : Even [", even ,"], Odd [", odd ,"] ", end = "")
		
	

def main() :
	obj = EvenOddNumber()
	# Test case
	obj.count_even_odd(2, 8)
	obj.count_even_odd(1, 10)
	obj.count_even_odd(21, 33)
	obj.count_even_odd(7, 29)
	obj.count_even_odd(0, 0)

if __name__ == "__main__": main()

Output

 Range [ 2 , 8 ] : Even [ 4 ], Odd [ 3 ]
 Range [ 1 , 10 ] : Even [ 5 ], Odd [ 5 ]
 Range [ 21 , 33 ] : Even [ 6 ], Odd [ 7 ]
 Range [ 7 , 29 ] : Even [ 11 ], Odd [ 12 ]
 Range [ 0 , 0 ] : Even [ 1 ], Odd [ 0 ]
#   Ruby program 
#   Count Even and Odd numbers in a range

class EvenOddNumber 
	# Count the number of Even and Odd elements in given range
	def count_even_odd(first, last) 
		if (first > last) 
			# Transform into a valid range
			self.count_even_odd(last, first)
		else 
			even = 0
			odd = 0
			# Count number of element
			length = (last - first) + 1
			if (first % 2 == 0) 
				if (last % 2 == 0) 
					# When both given number is even
					even = (length / 2) + 1
				else 
					even = length / 2
				end

				odd = length - even
			else 
				if (last % 2 != 0) 
					odd = (length / 2) + 1
				else 
					odd = length / 2
				end

				even = length - odd
			end

			print("\n Range [", first ,",", last ,"] : Even [", even ,"], Odd [", odd ,"] ")
		end

	end

end

def main() 
	obj = EvenOddNumber.new()
	# Test case
	obj.count_even_odd(2, 8)
	obj.count_even_odd(1, 10)
	obj.count_even_odd(21, 33)
	obj.count_even_odd(7, 29)
	obj.count_even_odd(0, 0)
end

main()

Output

 Range [2,8] : Even [4], Odd [3] 
 Range [1,10] : Even [5], Odd [5] 
 Range [21,33] : Even [6], Odd [7] 
 Range [7,29] : Even [11], Odd [12] 
 Range [0,0] : Even [1], Odd [0] 
/* 
  Scala program 
  Count Even and Odd numbers in a range
*/
class EvenOddNumber
{
	//Count the number of Even and Odd elements in given range
	def count_even_odd(first: Int, last: Int): Unit = {
		if (first > last)
		{
			//Transform into a valid range
			count_even_odd(last, first);
		}
		else
		{
			var even: Int = 0;
			var odd: Int = 0;
			//Count number of element
			var length: Int = (last - first) + 1;
			if (first % 2 == 0)
			{
				if (last % 2 == 0)
				{
					//When both given number is even
					even = ((length / 2).toInt) + 1;
				}
				else
				{
					even = (length / 2).toInt;
				}
				odd = length - even;
			}
			else
			{
				if (last % 2 != 0)
				{
					odd = ((length / 2).toInt) + 1;
				}
				else
				{
					odd = (length / 2).toInt;
				}
				even = length - odd;
			}
			print("\n Range [" + first + "," + last + "] : Even [" + even + "], Odd [" + odd + "] ");
		}
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		var obj: EvenOddNumber = new EvenOddNumber();
		//Test case
		obj.count_even_odd(2, 8);
		obj.count_even_odd(1, 10);
		obj.count_even_odd(21, 33);
		obj.count_even_odd(7, 29);
		obj.count_even_odd(0, 0);
	}
}

Output

 Range [2,8] : Even [4], Odd [3]
 Range [1,10] : Even [5], Odd [5]
 Range [21,33] : Even [6], Odd [7]
 Range [7,29] : Even [11], Odd [12]
 Range [0,0] : Even [1], Odd [0]
/* 
  Swift 4 program 
  Count Even and Odd numbers in a range
*/
class EvenOddNumber
{
	//Count the number of Even and Odd elements in given range
	func count_even_odd(_ first: Int, _ last: Int)
	{
		if (first > last)
		{
			//Transform into a valid range
			self.count_even_odd(last, first);
		}
		else
		{
			var even: Int = 0;
			var odd: Int = 0;
			//Count number of element
			let length: Int = (last - first) + 1;
			if (first % 2 == 0)
			{
				if (last % 2 == 0)
				{
					//When both given number is even
					even = (length / 2) + 1;
				}
				else
				{
					even = length / 2;
				}
				odd = length - even;
			}
			else
			{
				if (last % 2 != 0)
				{
					odd = (length / 2) + 1;
				}
				else
				{
					odd = length / 2;
				}
				even = length - odd;
			}
			print("\n Range [\(first,last)] : Even [", even ,"], Odd [", odd ,"]", terminator: "");
		}
	}
}
func main()
{
	let obj: EvenOddNumber = EvenOddNumber();
	//Test case
	obj.count_even_odd(2, 8);
	obj.count_even_odd(1, 10);
	obj.count_even_odd(21, 33);
	obj.count_even_odd(7, 29);
	obj.count_even_odd(0, 0);
}
main();

Output

 Range [(2, 8)] : Even [ 4 ], Odd [ 3 ]
 Range [(1, 10)] : Even [ 5 ], Odd [ 5 ]
 Range [(21, 33)] : Even [ 6 ], Odd [ 7 ]
 Range [(7, 29)] : Even [ 11 ], Odd [ 12 ]
 Range [(0, 0)] : Even [ 1 ], Odd [ 0 ]
Last updated on by Kalkicode




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