C# if, if...else, if...else if and Nested if Statement

In C#, conditional statements allow you to control the flow of program execution based on a condition. The most basic conditional statement is the if statement. In this article, we'll cover the if statement and its variations, including the if...else statement, the if...else if statement, and nested if statements.

The if Statement

The if statement is used to test a condition and execute a block of code if the condition is true. The syntax of the if statement is as follows:

1if (condition)
2{
3    // code to execute if the condition is true
4}

Here's an example:

1int x = 5;
2
3if (x > 0)
4{
5    Console.WriteLine("x is positive.");
6}

In this example, the if statement checks whether the value of x is greater than 0. If it is, the code inside the braces is executed, which prints "x is positive." to the console.

The if...else Statement

The if...else statement is used to test a condition and execute one block of code if the condition is true, and another block of code if the condition is false. The syntax of the if...else statement is as follows:

1if (condition)
2{
3    // code to execute if the condition is true
4}
5else
6{
7    // code to execute if the condition is false
8}

Here's an example:

1int x = -5;
2
3if (x > 0)
4{
5    Console.WriteLine("x is positive.");
6}
7else
8{
9    Console.WriteLine("x is not positive.");
10}

In this example, the if statement checks whether the value of x is greater than 0. If it is, the code inside the first set of braces is executed, which prints "x is positive." to the console. If it is not, the code inside the second set of braces is executed, which prints "x is not positive." to the console.

The if...else if Statement

The if...else if statement is used to test multiple conditions. It works like a series of nested if statements, with each if statement being tested in order until a condition is true. The syntax of the if...else if statement is as follows:

1if (condition1)
2{
3    // code to execute if condition1 is true
4}
5else if (condition2)
6{
7    // code to execute if condition2 is true
8}
9else if (condition3)
10{
11    // code to execute if condition3 is true
12}
13else
14{
15    // code to execute if none of the conditions are true
16}

Here's an example:

1int x = 0;
2
3if (x > 0)
4{
5    Console.WriteLine("x is positive.");
6}
7else if (x < 0)
8{
9    Console.WriteLine("x is negative.");
10}
11else
12{
13    Console.WriteLine("x is zero.");
14}

In this example, the if statement checks whether the value of x is greater than 0. If it is, the code inside the first set of braces is executed, which prints "x is positive." to the console. If it is not, the next else if statement is tested, which checks whether x is less than 0. If it is, the code inside the second set of braces is executed, which prints "x is negative." to the console. If it is not, the code inside the third block will execute.

Nested if Statements

You can also use if statements inside other if statements. This is called a nested if statement. The inner if statement is executed only if the outer if statement evaluates to true. Here is an example:

1int num1 = 5, num2 = 10, num3 = 15;
2if (num1 < num2)
3{
4    Console.WriteLine("num1 is less than num2");
5    if (num2 < num3)
6    {
7        Console.WriteLine("num2 is less than num3");
8    }
9}

In this example, the outer if statement checks whether num1 is less than num2. If it is true, it executes the code inside the if block. Inside the if block, there is another if statement that checks whether num2 is less than num3. If it is true, it executes the code inside the inner if block.

Nested if statements can be useful in situations where you need to test for multiple conditions. However, be careful not to make your code too complex or difficult to read.