An even number is a number that is exactly divisible by 2, while an odd number leaves a remainder of 1 or -1 when divided by 2.

For example, consider the following array:

const numbers = [10, 15, 20, 25, 30, 35, 40];

In this array, the even numbers are 10, 20, 30, 40 and the odd numbers are 15, 25, 35.

Therefore, the total count is:

• Even numbers: 4
• Odd numbers: 3

In this article, we will learn how to count even & odd numbers in a JavaScript array using different methods.

1. JavaScript Program to Count Even and Odd Numbers Using a For Loop

The for loop is one of the simplest methods for counting even and odd numbers in an array. We use the modulo operator (%) to determine whether each number is divisible by 2.

Program :

const numbers = [10, 15, 20, 25, 30, 35, 40];
let evenCount = 0;
let oddCount = 0;
for (let i = 0; i < numbers.length; i++) {
if (numbers[i] % 2 === 0) {
evenCount++;
} else {
oddCount++;
}
}
console.log("Even numbers count:", evenCount);
console.log("Odd numbers count:", oddCount);

Output :

Even numbers count: 4

Odd numbers count: 3

Explanation :

1. We create an array named numbers containing seven integers.
2. We initialize evenCount and oddCount to 0.
3. The for loop visits every element in the array.
4. The condition numbers[i] % 2 === 0 checks whether the current number is even.
5. If the condition is true, evenCount increases by one. Otherwise, oddCount increases by one.
6. Finally, we display both counts using console.log().

This approach is easy to understand and is suitable for beginners learning JavaScript loops and conditional statements.

2. JavaScript Program to Count Even and Odd Numbers Using a For…of Loop

The for…of loop provides a simple way to iterate over array values without using an index.

Program :

const numbers = [2, 7, 12, 19, 24, 31, 36];
let evenCount = 0;
let oddCount = 0;
for (const number of numbers) {
if (number % 2 === 0) {
evenCount++;
} else {
oddCount++;
}
}
console.log("Even numbers count:", evenCount);
console.log("Odd numbers count:", oddCount);

Output :

Even numbers count: 4

Odd numbers count: 3

Explanation :

The for…of loop assigns each array value to the variable number. The modulo operator checks whether that value is even or odd.

This method avoids manually managing an index and makes the program more readable.

3. JavaScript Program to Count Even and Odd Numbers Using forEach()

The forEach() method executes a callback function for every element in an array. We can use it to check each number and update the appropriate counter.

Program :

const numbers = [11, 14, 17, 20, 23, 26, 29, 32];
let evenCount = 0;
let oddCount = 0;
numbers.forEach(function (number) {
if (number % 2 === 0) {
evenCount++;
} else {
oddCount++;
}
});
console.log("Even numbers count:", evenCount);
console.log("Odd numbers count:", oddCount);

Output :

Even numbers count: 4

Odd numbers count: 4

Explanation :

The forEach() method passes each array element to the callback function. Inside the function, the modulo operator determines whether the number is even or odd.

The corresponding counter is incremented until every array element has been processed.

We can also use an arrow function, although the regular callback above is often easier for beginners to read.

JavaScript Program to Count Even and Odd Numbers in an Array was originally published in JavaScript in Plain English on Medium, where people are continuing the conversation by highlighting and responding to this story.

The decimal number system uses base 10 and contains digits from 0 to 9. In contrast, the binary number system uses base 2 and contains only two digits: 0 and 1. Computers use binary representation to process and store data.

For example, the decimal number 10 is represented as 1010 in binary.

In this article, we will learn how to convert a decimal number to binary in JavaScript using different methods.

1. JavaScript Program to Convert Decimal to Binary Using a While Loop

The while loop is a simple way to convert a decimal integer to binary. The basic idea is to repeatedly divide the number by 2 and record the remainder.

Program :

function decimalToBinary(decimal) {
if (!Number.isSafeInteger(decimal) || decimal < 0) {
throw new Error("Please enter a non-negative integer.");
}
if (decimal === 0) {
return "0";
}
let binary = "";
while (decimal > 0) {
let remainder = decimal % 2;
binary = remainder + binary;
decimal = Math.floor(decimal / 2);
}
return binary;
}
console.log(decimalToBinary(10));
console.log(decimalToBinary(25));
console.log(decimalToBinary(50));

Output :

1010

11001

110010

Explanation :

1. The decimalToBinary() function accepts a decimal integer.
2. It checks that the input is a non-negative integer.
3. If the input is 0, the function returns “0” immediately.
4. The while loop runs as long as the decimal number is greater than zero.
5. The modulo operator (%) calculates the remainder when the number is divided by 2.
6. The remainder is added to the beginning of the binary string.
7. Math.floor() divides the number by 2 and rounds the result down to an integer.
8. The loop stops when the number becomes zero and the function returns the binary representation.

The remainder digits are generated from right to left, which is why each new remainder is added to the beginning of the string.

2. JavaScript Program to Convert Decimal to Binary Using the toString() Method

The JavaScript provides a built-in toString() method that can convert a number into a string representation.

Program :

const decimal = 10;
const binary = decimal.toString(2);
console.log("Decimal number:", decimal);
console.log("Binary number:", binary);

Output :

Decimal number: 10

Binary number: 1010

Explanation :

The toString(2) method converts the number into its base-2 representation.

For example:

console.log((5).toString(2)); // 101

console.log((12).toString(2)); // 1100

console.log((20).toString(2)); // 10100

console.log((100).toString(2)); // 1100100

3. JavaScript Program to Convert Decimal to Binary Using a For Loop

A for loop can also perform decimal-to-binary conversion. The loop repeatedly calculates the remainder and divides the number by 2.

Program :

function decimalToBinary(decimal) {
if (!Number.isSafeInteger(decimal) || decimal < 0) {
throw new Error("Please enter a non-negative safe integer.");
}
if (decimal === 0) {
return "0";
}
let binary = "";
for (; decimal > 0; decimal = Math.floor(decimal / 2)) {
binary = (decimal % 2) + binary;
}
return binary;
}
console.log("Binary:", decimalToBinary(18));

Output :

Binary: 10010

JavaScript Program to Convert Decimal to Binary was originally published in JavaScript in Plain English on Medium, where people are continuing the conversation by highlighting and responding to this story.