**1. Check if a number is odd or even in JavaScript**

Function `isEvenOrOdd()` checks if input number is even or odd by using “%” operator in JavaScript.

- Print “Number is even” if the number is divisible by 2.
- Else print “Number is odd” if the number returns a remainder when divided by 2.

```
function isEvenorOdd(num) {
if(num % 2 == 0){
console.log(`${num} is a Even number`)
}
else{
console.log(`${num} is a Odd number`)
}
}
isEvenorOdd(10) //"10 is a Even number"
isEvenorOdd(19) //"19 is a Odd number"
```

**2. Check if input variable is a number or not**

Function `isNumber()` checks if input variable is a number by using isNaN() in-built JavaScript function. Read more about isNan() from w3schools.com/jsref/jsref_isnan.asp.

- Print “Variable is not a number” if isNaN() returns true.
- Else print “Variable is a valid number” if isNaN() returns false.

```
function isValidNumber(num) {
if(isNaN(num)){
console.log(`${num} is not a number`)
}
else{
console.log(`${num} is a valid number`)
}
}
isValidNumber(11) //"11 is a valid number"
isValidNumber("19") //"19 is a valid number"
isValidNumber("xyz") //"xyz is not a number"
isValidNumber("17.5") //"17.5 is a valid number"
isValidNumber("21F") //"21F is not a number"
```

**3. Find the largest of two number**

Function `findLargest()` finds the largest between two number by using “>” and “=” operator in JavaScript.

- Print num1 is the largest if num1>num2.
- Print num2 is the largest if num1<num2.
- Else print num1 and num2 are equal when num1==num2.

```
function findLargest(num1, num2) {
if(num1 > num2){
console.log(`${num1} is the largest number`)
}
else if (num2 > num1){
console.log(`${num2} the largest number`)
}
else{
console.log(`${num1} is equal to ${num2}`)
}
}
findLargest(21,45) //"45 the largest number"
findLargest(34,18) //"34 is the largest number"
findLargest(41,41) //"41 is equal to 41"
```

**4. Find the largest of three number**

Function `findLargest()` finds the largest of three number by using “>” and “&&” operator in JavaScript.

- Print num1 is the largest if num1>num2 and num1>num3.
- Print num2 is the largest if num2<num3.
- Else print num3.

```
function findLargest(num1, num2, num3) {
if(num1 > num2 && num1 > num3){
console.log(`${num1} is the largest number`)
}
else if (num2 > num3){
console.log(`${num2} is the largest number`)
}
else{
console.log(`${num3} is the largest number`)
}
}
findLargest(21,45,13) //"45 is the largest number"
findLargest(34,18,52) //"52 is the largest number"
findLargest(64,11,11) //"64 is the largest number"
```

**5. Check if a triangle is equilateral, scalene, or isosceles**

Function `findTriangleType()` finds the type of the triangle for given side values by using “==” and “&&” operator in JavaScript.

- Print “Equilateral triangle.” if values for all side1, side2 and side3 are equal.
- Print “Isosceles triangle.” if values for side1 is equal to side2 or side2 is equal to side3
- Else “Scalene triangle.” since values of all sides are unequal.

```
function findTriangleType(side1, side2, side3) {
if((side1 == side2) && (side1 == side3)){
console.log(`Equilateral triangle.`)
}
else if ((side1 == side2) || (side2 == side3)){
console.log(`Isosceles triangle.`)
}
else{
console.log(`Scalene triangle.`)
}
}
findTriangleType(12,12,12) //"Equilateral triangle."
findTriangleType(20,20,31) //"Isosceles triangle."
findTriangleType(5,4,3) //"Scalene triangle."
```

**6. Find the a number is present in given range**

Function `checkInRange()` finds if the given number is within the provided start and end range using >=, <= and && operators in JavaScript.

- Print “Between the range” if num is between start and end values
- Else Print “Outside the range” since num is outside start and end values.

```
function checkInRange(num, start, end) {
if(num >= start && num <= end){
console.log(`${num} is between the range ${start} and ${end}`)
}
else{
console.log(`${num} is outside the range ${start} and ${end}`)
}
}
checkInRange(15,11,30) //"15 is between the range 11 and 30"
checkInRange(20,34,51) //"20 is outside the range 34 and 51"
```

**7. Perform ****arithmetic** operations on two numbers

**arithmetic**operations on two numbers

Function `evalNumbers()` prints the result after evaluating arithmetic operations between two numbers of addition, multiplication, division, and modulus in JavaScript.

- Print result of num1+num2 if operation is “add”
- Print result of num1-num2 if operation is “subtract”
- Print result of num1*num2 if operation is “multiply”
- Print result of num1/num2 if operation is “divide”
- Print result of num1%num2 if operation is “modulus”
- Else print “Invalid operation”

```
function evalNumbers(num1, num2, op) {
if(op == "add"){
console.log(`Sum of ${num1} and ${num2} is ${num1+num2}`)
}
else if(op == "subtract"){
console.log(`Difference of ${num1} and ${num2} is ${num1-num2}`)
}
else if(op == "multiply"){
console.log(`Product of ${num1} and ${num2} is ${num1*num2}`)
}
else if(op == "divide"){
console.log(`Division of ${num1} and ${num2} is ${num1/num2}`)
}
else if(op == "modulus"){
console.log(`Modulus of ${num1} and ${num2} is ${num1%num2}`)
}
else{
console.log(`${op} is an invalid operation`)
}
}
evalNumbers(15,10,"add") //"Sum of 15 and 10 is 25"
evalNumbers(20,8,"subtract") //"Difference of 20 and 8 is 12"
evalNumbers(12,4,"multiply") //"Product of 12 and 4 is 48"
evalNumbers(28,7,"divide") //"Division of 28 and 7 is 4"
evalNumbers(22,3,"modulus") //"Modulus of 22 and 3 is 1"
evalNumbers(31,3,"square") //"square is an invalid operation"
```

**8. Find check if a year is leap year or not**

Function `checkLeapYear()` find if the given year is a leap year or not by using %, !=, && and || operators in JavaScript.

- If year is divisble by 4 and not divisble by 100 then print “leap year”.
- Or if year is divisible by 400 then print “leap year”.
- Else print “not a leap year”.

```
function checkLeapYear(year) {
if(((year%4 == 0)&&(year%100 != 0))||(year%400 == 0)){
console.log(`Year ${year} is a leap year`);
}
else{
console.log(`Year ${year} is not a leap year`);
}
}
checkLeapYear(2012) //"Year 2012 is a leap year"
checkLeapYear(1900) //"Year 1900 is not a leap year"
checkLeapYear(2000) //"Year 2000 is a leap year"
checkLeapYear(2011) //"Year 2011 is not a leap year"
```

**9. Find the grade for input marks**

Function `findGrade()` to find the grade of the student based on the input marks.

- Print “S grade” if marks is between 90 and 100.
- Print “A grade” if marks is between 80 and 90.
- Print “B grade” if marks is between 70 and 80.
- Print “C grade” if marks is between 60 and 70.
- Print “D grade” if marks is between 50 and 60.
- Print “E grade” if marks is between 40 and 50.
- Print “Student has failed” if marks is between 0 and 40.
- Else print “Invalid marks”.

```
function findGrade(name, marks) {
if(marks >= 90 && marks <= 100){
console.log(`${name} you have received S grade`)
}
else if(marks >= 80 && marks < 90){
console.log(`${name} you have received A grade`)
}
else if(marks >= 70 && marks < 80){
console.log(`${name} you have received B grade`)
}
else if(marks >= 60 && marks < 70){
console.log(`${name} you have received C grade`)
}
else if(marks >= 50 && marks < 60){
console.log(`${name} you have received D grade`)
}
else if(marks >= 40 && marks < 50){
console.log(`${name} you have received E grade`)
}
else if(marks >= 0 && marks <40){
console.log(`${name} you have Failed`)
}
else{
console.log(`Invalid marks of ${marks}`)
}
}
findGrade("John Doe", 91) //"John Doe you have received S grade"
findGrade("John Doe", 85) //"John Doe you have received A grade"
findGrade("John Doe", 73) //"John Doe you have received B grade"
findGrade("John Doe", 53) //"John Doe you have received D grade"
findGrade("John Doe", 20) //"John Doe you have Failed"
findGrade("John Doe", 120) //"Invalid marks of 120"
```

**10. Find number of days in a given month**

Function `findDaysInMonth()` finds the number of days in a given month of a year.

- If month is outside the range of 1 and 12 print “Invalid month”.
- If month is equal to 2 ie, February print “29 days” if leap year else print “28 days” .
- Else if month is equal to 4, 6, 9 or 11 print “30 days”.
- Else print “31 days”.

```
function isLeapYear(year){
return (((year%4 == 0)&&(year%100 != 0))||(year%400 == 0));
}
function findDaysInMonth(month, year) {
if(month < 1 || month > 12){
console.log(`Invalid Month of value ${month}`)
return;
}
if(month ==2){
if(isLeapYear(year)){
console.log(`The Month has 29 days`)
}
else{
console.log(`The Month has 28 days`)
}
}
else if(month == 4 || month == 6 || month == 9 || month== 11){
console.log(`The Month has 30 days`)
}
else{
console.log(`The Month has 31 days`)
}
}
findDaysInMonth(2, 2012) //"The Month has 29 days"
findDaysInMonth(2, 2013) //"The Month has 28 days"
findDaysInMonth(4, 2012) //"The Month has 30 days'
findDaysInMonth(10, 2013) //"The Month has 31 days"
```

**Video for Reference**