csharp-basics/3. Conditionals.md

# Conditionals

![](imgs/3%20Conditionals_0.png)

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# Overview

Conditionals

if and else

Logical Operators

# Conditionals

Less than: 				a < b

Less than or equal to: 		a <= b

Greater than: 				a > b

Greater than or equal to:	a >= b

Equal to 					a == b

Not Equal to: 				a != b

Conditionals return true or false, meaning the result can even be allocated into a variable if needed

bool areEqual = (a == b);

# if , else and else if statements

double temperatureInOulu = 2.3;

double temperatureInIvalo = -10.9;

if (temperatureInOulu > temperatureInIvalo)

{

Console.WriteLine("Oulu is warmer than Ivalo");

}

else if (temperatureInOulu < temperatureInIvalo)

{

Console.WriteLine("Ivalo is warmer than Oulu");

}

else

{

Console.WriteLine

("Oulu and Ivalo have the same temperature");

}

__if __ statements are executed in order

The first statement with a  __true __ condition is executed

If no statement holds a true value,  __else __ is executed

This outputs "Oulu is warmer than Ivalo"

# ! -Operator

Console.WriteLine(!true);       // Outputs false

bool itsColdOutside = true;

if(!itsColdOutside)

{

Console.WriteLine("It's warm outside.");

}

The ! -operator flips the boolean value __ __

# The switch statement

The  __switch __ statement compares the parameter value (here: the  __path __ variable) with the value of each  __case__

Only the matching code is executed

If no match is found, the default code block is executed

This outputs "Here's the catalogue!"

break ends the case and exits the switch: the code will not compile if omitted

string path = "/browse";

switch (path)

{

case "/browse":

Console.WriteLine("Here's the catalogue!");

break;

case "/contact":

Console.WriteLine("Here's our contact info.");

break;

default:

Console.WriteLine("No such path!");

break;

}

# Scope of Variables

Variables declared inside of blocks are called  __local variables__ ; they are only accessible inside of that block.

int a = 0;

if(a < 10)

{

// Variable 'b' is only accessible inside of this if block

int b = 1;

b = 2;          // This works

}

b = 3;              // This throws an error

# Assignment Operators

We have used the assignment operator ' __='__  for assigning values for variables:

int x;

x = 25;

__Notice __ the difference between '=' and the conditional '=='!

'=' is used for assigning values for variables, '== is used for comparing values

# Logical Operators

'&&', '||' and '!' mean the logical AND, OR and NOT operators

For example,

int a = 1;

int b = 3;

int c = 5;

Console.WriteLine(a < b && a < c);

outputs "True"

| Operator | Name | Example | Description |
| :-: | :-: | :-: | :-: |
| && | AND | a && b | Returns true if  __both__  variables are true.b is not evaluated if a == false. |
| || | OR | a || b | Returns true if  __one or both__  variables are true. b is not evaluated if a == true. |
| ! | NOT | !a | __Negates__  boolean value (true becomes false and vice versa) |
| ^ | XOR | a ^ b | Exclusive OR: returns true if  __only __ a == true  __OR only__  b == true. |
| & | Logical AND | a & b | Returns true if  __both__  variables are true. Both variables are always evaluated. |
| | | Logical OR | a | b | Returns true if  __one or both__  variables are true.Both variables are always evaluated. |

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Tässä on kaikki aritmeettiset operaattorit

# Operators - Example

This outputs "Strong password!"

int uppercaseLetters = 2;

uppercaseLetters += 4;          // is now 6

int specialCharacters = 2;

specialCharacters *= 2;         // is now 4

if (uppercaseLetters >= 6 && specialCharacters >= 2)

{

Console.WriteLine("Strong password!");

}

else

{

Console.WriteLine("Weak-ass password...");

}

# Exercise 1:

Create a console application which asks the user which weekday it is and assigns the answer to a string variable.

Using a switch-case, calculate the days remaining until next Monday.

If the result is more than 3, print "Have a nice week!". Otherwise, print "Have a nice weekend!".

# Exercise 2:

Create a console application which lets the user input a note.

If the length of the note is less than 30, the program prints the current time and the note, separated with a tab. Otherwise, the date and the note are printed to a separate line.

Tip: Use DateTime.Now.ToString() for current time. Use .Length after your message variable to get the length of the message.

# One More Thing...

If a code block following a statement only has one line of code, you can write the code without using curly brackets:

int baa = 49;

if (baa > 20)

Console.WriteLine("Baa");

else

Console.WriteLine("Not baa!");

if (baa > 20) Console.WriteLine("Baa");

else Console.WriteLine("Not baa!");

You may see code where this is done. However, we highly recommend you not to use this syntax as it is highly prone to  [errors](https://www.leadingagile.com/2018/01/the-goto-fail-bug-as-a-coaching-tool/) .

# Get Help

All the basics covering the syntax in C# are covered here:

[https://www.tutorialspoint.com/csharp/index.](https://www.tutorialspoint.com/csharp/index.htm)  [htm](https://www.tutorialspoint.com/csharp/index.htm)  [l](https://www.tutorialspoint.com/csharp/index.htm)

[https://www.w3schools.com/cs/default.asp](https://www.w3schools.com/cs/default.asp)

# Assignments

[Assignments about this topic can be found here](https://gitea.buutti.com/education/academy-assignments/src/branch/master/C%23%20Basics/3.%20Conditionals)