PHP Flow control functions

• IF statement - As the name implies, the code enclosed in parenthesis following an if statement is only executed when the condition in the IF statement returns TRUE. If the condition evaluates to FALSE the code enclosed in the parenthesis following the else keyword is executed.
format for the IF statement:


  $age = 15;

  if($age >=10 && $age <= 15){

     echo “Must have 200g of Calcium per day”;

}else{

       echo “check the other conditions and take appropriate action”;

}


This code here will evaluate the value in the variable $age, if that value is between 10 and 15 it will display Must have 200g of Calcium per day, otherwise display check the other conditions and take appropriate action . In this case, because we assigned the value 15 to the variable $age, the first statement will be executed. If we assigned the value 25 to the variable age, the statement enclosed in the ELSE parenthesis would be executed.


• ( ? )Operator otherwise known as ternary operator - Is very similar to the IF statement, the returned value is derived from one of the expressions separated by a colon (:) . Example of ternary operator usage:

expression ? returned_if expression_is_true : 
 returned_if_expresion_is_false 


Now, let us try to evaluate our expression from the previous example using the ternary operator:


$output = ($age >=10 && $age <= 15) ? “200g Calcium” : “Further evaluation”; 
          echo $output;
  

This statement will evaluate whether the value of $age is greater than or equal to 10 AND less than or equal to 15. Since the assigned value (from previous example) is 15, the expression evaluates to TRUE and thus the first or expression to the left of the colon ( : ) will be returned and displayed on the screen.

• Switch Statement - Unlike the IF statement, which if used with else if may yields multiple expression, the switch statement only evaluates to a single expression and executes different code components depending on the result of that expression. Bellow is an example of a switch statement usage:




switch ($gender){
         case ‘Male’ :  echo “person in question is a Man”;
                       break;
         case ‘Female’ : echo “person in question is a Woman”;
                       break;
         default : echo “the gender of the person in question could not be determined”;
                   break;
          }


Which statement is displayed is dependant on the value of the variable $gender. If that Variable has the value “Male” then the statement person in question is a Man will be displayed. If the value is female then person in question is a Woman is displayed. Should the variable $gender not be assigned any value or if the value in the variable is neither “Male” nor “Female” then the statement the gender of the person in question could not be determined will be displayed.