If-else statements

If-else statements

You can use if statements to run code statement only if certain conditions are met. Here is an example:

var myNum = (93 + 41) / 12;
if (myNum == 11)
{
    Console.WriteLine("They are equal!");
}

Inside the () beside if, you should specify a boolean expression. If the expression is true, the code inside { } is executed. In this case, since myNum is equal to 11, They are equal! is printed.

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If the condition is false, nothing happens! For example, since 10 is not greater than 11, Print me! will not show up to the console.

var happy = 10;
if (happy > 11)
{
    Console.WriteLine("Print me!");
}

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Use else to tell the computer what to do if the condition is false. In this example, now I got printed instead! will be printed to the console.

var happy = 10;
if (happy > 11)
{
    Console.WriteLine("Print me!");
}
else
{
    Console.WriteLine("I got printed instead!");
}

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You can chain many cases together using else if. Note that when using else if, only the first case will be evaluated. For example, in the following code snippet, Statement 1 will be printed. We will skip the check that sad == 4 and Statement 2 will not be printed, even though sad == 4 is true.

var sad = 4;
if (sad < 9)
{
    Console.WriteLine("Statement 1");
}
else if (sad == 4)
{
    Console.WriteLine("Statement 2");
}
else
{
    Console.WriteLine("Statement 3");
}

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You can also place if statements inside other if statements for some interesting behavior:

var num1 = 10;
var num2 = 20;
if (num1 < num2)
{
    if (num2 < 30)
    {
        Console.WriteLine("Hello!");
    }
    else
    {
        Console.WriteLine("Hola!");
    }
}

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Working Together

Let’s write a program that first prints the following line to console:

Is coding fun?

Afterwards, the console waits for user input.

  • If the user enters yes, the computer prints out Yes, I'm glad you're enjoying it!.
  • If the user enters no, the computer prints out Oh no, that's too bad!.
  • Otherwise, the computer prints out: I don't understand you! Goodbye!.

Fun Fact: Switch statements

Using multiple if, else statements could get very long and confusing. You can use switch statements instead if you want to compare a single variable against multiple values. For example, the Working Together activity can be completed using the following piece of code:

    var input = Console.ReadLine();
    switch (input)
    {
        case "yes":
            Console.WriteLine("Yes, I'm glad you're enjoying it!");
            break;
        case "no":
            Console.WriteLine("Oh no, that's too bad!");
            break;
        default:
            Console.WriteLine("I don't understand you! Goodbye!");
            break;
    }

Each case represents a possible value that the variable input might take. Make sure you use the break statement to tell the computer that you have completed all the actions associated with this case.