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This article is currently in the process of being translated into Polish (~5% done).

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Instrukcja if

One of the single most important statements in every programming language is the if statement. Being able to set up conditional blocks of code is a fundamental principal of writing software. In C#, the if statement is very simple to use. If you have already used another programming language, chances are that you can use the if statement in C# straight away. In any case, read on to see how it's used. The if statement needs a boolean result, that is, true or false. In some programming languages, several datatypes can be automatically converted into booleans, but in C#, you have to specifically make the result boolean. For instance, you can't use if(number), but you can compare a number to something, to generate a true or false, like we do later on.

W poprzednim rozdziale przyjrzeliśmy się zmiennym, więc rozwiniemy jeden z przykładów, aby zobaczyć, jak można użyć logiki warunkowej.

using System;

namespace ConsoleApplication1
{
    class Program
    {
static void Main(string[] args)
{
    int number;

    Console.WriteLine("Please enter a number between 0 and 10:");
    number = int.Parse(Console.ReadLine());

    if(number > 10)
Console.WriteLine("Hey! The number should be 10 or less!");
    else
if(number < 0)
    Console.WriteLine("Hey! The number should be 0 or more!");
else
    Console.WriteLine("Good job!");

    Console.ReadLine();
}
    }
}

We use 2 if statements to check if the entered number is between 0 and 10, and a companion of the if statement: The else keyword. Its meaning should be obvious to anyone speaking English - it simply offers an alternative to the code being executed if the condition of the if statement is not met.

As you may have noticed, we don't use the { and } characters to define the conditional blocks of code. The rule is that if a block only contains a single line of code, the block characters are not required. Now, this seems like a lot of lines to simply check a number, doesn't it? It can be done with fewer lines of code, like this:

if((number > 10) || (number < 0))
    Console.WriteLine("Hey! The number should be 0 or more and 10 or less!");
else
    Console.WriteLine("Good job!");

We put each condition in a set of parentheses, and then we use the || operator, which simply means "or", to check if the number is either more than 10 OR less than 0. Another operator you will be using a lot is the AND operator, which is written like this: &&. Could we have used the AND operator instead? Of course, we simply turn it around a bit, like this:

if((number <= 10) && (number >= 0))
    Console.WriteLine("Good job!");
else
    Console.WriteLine("Hey! The number should be 0 or more and 10 or less!");

This introduces a couple of new operators, the "less than or equal to" and the "greater than or equal to".

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