====== Program control structures ======

===== Control structure =====
**If** is a statement that checks the condition and executes the following statements if the condition is //true//. There are multiple ways how to write down the //if// statement:

<code c>
//1st example
if (condition) statement;     

//2nd example
if (condition)
statement;                    

//3rd example
if (condition) { statement; } 

//4th example
if (condition)
{
  statement;
}                             
</code>

When both //true// and //false// cases of the condition should be viewed, the **else** part should is added to the //if// statement in the following ways:

<code c>
if (condition) {
  statement1;    //executes when the condition is true
}
else {
  statement2;    //executes when the condition is false
}
</code>

If more conditions should be viewed, the **else if** part is added to the //if// statement:
<code c>
if (condition1) {
  statement1;    //executes when the condition1 is true
}
else if (condition2) {
  statement2;    //executes when the condition2 is true
}
else {
  statement3;      //executes in all of the rest cases
}
</code>

The example when the //x// variable is compared and in the cases when it is higher than //10//, the //digitalWrite()// method executes. 
<code c>
if (x>10) 
{
  digitalWrite(LEDpin, HIGH)  //statement is executed if the x>10 expression is true
}
</code>


===== Logical operators =====
Logical operators are widely used together with the condition operator //if// that is described below.

==== Comparison operators ====
There are multiple comparison operators used for comparing variables and values. All of these operators compare the value of the variable on the left to the value of the variable on the right. Comparison operators are following:
  * == (equal to) -  if they are equal, the result is //TRUE//, otherwise //FALSE//.
  * != (not equal to) - if they are not equal, the result is //TRUE//, otherwise //FALSE//.
  * < (less than) - if the value of the variable on the left is less than the value of the variable on the right, the result is //TRUE//, otherwise //FALSE//.
  * < = (less than or equal to) - if the value of the variable on the left is less than or equal to the value of the variable on the right, the result is //TRUE//, otherwise //FALSE//.
  * > (greater than) - if the value of the variable on the left is greater than the value of the variable on the right, the result is //TRUE//, otherwise //FALSE//.
  * > = (greater than or equal to) - if the value of the variable on the left is greater than or equal to the value of the variable on the right, the result is //TRUE//, otherwise //FALSE//.

Examples:
<code c>
if (x==y){ //equal
  //statement
}

if (x!=y){ //not equal
  //statement
}

if (x<y){ //less than
  //statement
}

if (x<=y){ //less than or equal
  //statement
}

if (x>y){ //greater than
  //statement
}

if (x>=y){ //greater than or equal
  //statement
}
</code>

==== Boolean operators ====
Three Boolean logical operators in the Arduino environment are following:
  * ! (logical NOT) - reverses the logical state of the operand. If a condition is //TRUE// the logical NOT operator will turn it to //FALSE// and the other way around.
  * && (logical AND) - the result is //TRUE// when the both operands on the left and on the right of the operator are //TRUE//. If even one of them is //FALSE// the result is //FALSE//.
  * || (logical OR) - result is //TRUE// when at least one of the operands on the left and on the right of the operator is //TRUE//. If both of them are //FALSE// the result is //FALSE//.

Examples:
<code c>
//logical NOT
if (!a) { //the statement inside "if" will execute when the "a" is FALSE
  b = !a; //the reverse logical value of "a" is assigned to the variable "b"
}

//logical AND
if (a && b){  //the statement inside "if" will execute when the values both of the "a" and "b" are TRUE
  //statement
}

//logical OR
if (a || b){  //the statement inside "if" will execute when at least one of the "a" and "b" values is TRUE
  //statement
}
</code>


===== Switch case statement =====
Switch statement similar like //if// statement controls the flow of program. The code inside //switch// is executed in various conditions. A //switch// statement compares the values of a variable to the specified values in the //case// statements. Allowed data types of the variable are //int// and //char//. The //break// keyword exits the //switch// statement.

Examples:
<code c>
switch (x) { 
   case 0:  //executes when the value of x is 0
   // statements
   break;   //goes out of the switch statement

   case 1:  //executes when the value of x is 1
   // statements
   break;   //goes out of the switch statement

   default:  //executes when none of the cases above is true
   // statements
   break;   //goes out of the switch statement
}
</code>


**Check yourself**
1. Which code part is correct?

  * if (value == 1) digitalWrite(13, HIGH)
  * if (value == 1); digitalWrite(13, HIGH)
  * if (value == 1) DigitalRead(13,1)
2. What is the output of the next code part?

<code c>
int x = 0;
 
    switch(x)
    {
 
      case 1: cout << "One";
 
      case 0: cout << "Two";
 
      case 2: cout << "Hello, world!";
 
    }
    </code>
3. In which cases 'switch structure' should be used?