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Comparision Operation & If-Else

This introduces different comparison operators such as ==, !=, >, <, etc that can be used in JavaScript and which data types they can be applied to.

The conditions tested are specified using comparison operators. These operators cause the immediate statement in which they are contained to return a Boolean value of either true or false.

The following comparison operators are available:

  • Equality: ==, or Inequality: != of any primitive data type (int, char, float, bool, etc.) These are binary operators (take two operands) and are specified using infix notation (which means that the operator goes in between the two operands).
  • Greater-than: >, Greater than or equal to: >=, Less-than: < and Less than or equal to: <= are also binary operators using infix notation.
  • Negation: ! is a unary operator, and prefixes the operand.

Examples

Statement Result
10 == 10 true
9 != 6 true
!true false
10 > 12 false

 

Now that you’re familiar with the comparison operators let’s look at the conditional statements.

As the name implies, conditional statements specify whether another statement or block of statements should be executed or not. These are often called “selection constructs”. The two general types are:

  • "if…then"
  • the "switch…case" construct

if, if-else and Nested if…else

There are three forms of if…else statements in JavaScript.

  1. if statement
  2. if...else statement
  3. if...else if...else statement

if statement

The syntax of the if statement is:

if (condition) {
// body of if statement
}

The if statement evaluates the condition inside the parentheses ( ).

  • If the condition evaluates to true, the code inside the body of if is executed.
  • If the condition evaluates to false, the code inside the body of if is skipped.

Example:

//Suppose num1 = 0 and num2 = 1,
if(num1 == 0){
console.log("num1 is equal to 0")
}
if(num2 == 0){
console.log("num1 is equal to 0")
}
// Body of first if is executed.
// prints num1 is equal to 0

if…else statement

The if statement can have an optional else clause. Its syntax is:

if (condition) {
// block of code if condition is true
}
else {
// block of code if condition is false
}

If the condition evaluates true,

  • the code inside the body of if is executed
  • the code inside the body of else is skipped from execution

If the condition evaluates false,

  • the code inside the body of else is executed
  • the code inside the body of if is skipped from execution

Example:

int num = 1;
if(num == 0){
console.log("num is equal to 0")
}
else{
console.log("num is not equal to 0")
}
// Body of else is executed.
// prints num is not equal to 0

if…else…else if statement

The if...else statement is used to execute a block of code among two alternatives. However, if we need to make a choice between more than two alternatives, we use the if...else if...else statement.

The syntax of the if...else if...else statement is:

if (condition1) {
// code block 1
}
else if (condition2){
// code block 2
}
else {
// code block 3
}

Here,

  • If condition1 evaluates to true, code block 1 is executed.
  • If condition1 evaluates to false, then condition2 is evaluated.
  • If condition2 is true, code block 2 is executed.
  • If condition2 is false, the code block 3 is executed

Example:

int num = 0;
if(num > 0){
console.log("num is greater than 0");
}
else if(num < 0){
console.log("num is lesser than 0")
}
else{
console.log("num is equal to 0")
}
// Body of else is executed.
// prints num is not equal to 0

Try the following example in the editor below.

Given an integer num denoting the percentage of a student, calculate the grade according to the below rules:

If num >= 90, grade A.
If num >= 80, grade B.
If num >= 70, grade C.
If num >= 60, grade D.
If num >= 50, grade E.
Else grade will be F.

Print a string consisting of a single character denoting the grade.

Sample Input

59

Sample Output

E
Start solving Comparision Operation & If-Else on Interview Code Editor
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