MS3304: Week 6 Conditional statements. Overview The flow of control through a script Boolean Logic...
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Transcript of MS3304: Week 6 Conditional statements. Overview The flow of control through a script Boolean Logic...
Overview
• The flow of control through a script• Boolean Logic• Conditional & logical operators • Basic decision making statements in PHP• Complex decision making statements in
PHP• Other uses of if statements• Advanced topic introduction: the
switch statement
Program flow of control
• Order of statement execution is called the flow of control
• Default order of execution of programming statements is linear
• Some statements (conditional) can modify the order of execution
• Conditional statements are based on Boolean logic
Conditional statements
• Conditional statements allow the script to decide which statement will be executed next
• Conditional statements in PHP are:– if– else– elseif
Overview of an the if statement
The basic if statement has the following syntax
if (condition){
statement;
}
if is a PHP reserved word The condition is a Boolean expression that can be evaluated as true or false
If the condition is true,this statement is executed
Boolean logic
• Developed by George Boole in mid 1800s
• All Boolean logic is based on the evaluation of statements
• These statement can either be evaluated as true or false
• Conditional and logical operators are used to create these statements
Boolean logic example
Assuming we have the following variables:
$CW1
$CW2
$CWAverage = ($CW1+$CW2)/2
What logical statements, in plain English, can we make to tell students at UEL if they have passed or need to do a resit?
Comparative and logical operators
Comparative == equal to!= not equal to< less than> greater than<= less than or equal to>= greater than or
equal to
Logical! NOT&& AND|| OR
Comparative and logical operators example 1if ($CW1=="NS"){
echo "CW1: 0 - <b>Resit</b>(not submitted). <br>\n";}if($CW1<30){
echo "CW1: $CW1 - <b>Resit</b> (below 30) .<br>\n";}if(($CW1>29) && ($CW1<40)){
echo "CW1: $CW1 - not passed, but threshold met.<br>\n";
}if ($CW1<40){
echo "CW1 passed.<br>\n";}
Comparative and logical operators example 2
if ( ($CW1<30 || $CW1 == "NS")|| ($CW2<30 || $CW2 == "NS") || ($CWAverage <40) ){ echo "You have not passed
the module and must resit at least one of the of
the pieces of CW.";}
Comparative and logical operators example 3
if ( ($CW1>=30 && $CW1!="NS")
&& ($CW2>=30 && $CW2!="NS")
&& ($CWAverage>=40) ){
echo "You have passed the module with a mark of $CWAverage.";
}
Overview of an the if/else statement
The basic if/else statement has the following syntax
if (condition){
statements;
} else{
statements;
}
If the condition is true these statements are executed
If the initial condition is false then the second block of statements is executed
if/else statements
if ( ($CW1>=30 && $CW1!="NS") && ($CW2>=30 && $CW2!="NS") && ($CWAverage>=40) ){echo "You have passed the module!"
}else{echo "You have not passed the module and must resit at least one of the of the pieces of CW.";
}
Overview of an the if/elseif statement
The basic if/else statement has the following syntax
if (condition){statements;
} elseif (condition){statements;
} else{statements;
}
If the condition is true these statements are executed
If neither of the conditions are true, then these statements are executed
If the first condition is false it tests the second condition, its true these statements are executed.
if/elseif statementsif ($CW1=="NS"){echo "CW1: 0 - <b>Resit</b> (not submitted).<br>\n";
}elseif($CW1<30){echo "CW1: $CW1 - <b>Resit</b> (below 30) .<br>\n";
}elseif(($CW1>29) && ($CW1<40)){echo "CW1: $CW1 - not passed, but threshold met.<br>\n";
}else{echo "CW1: $CW1 - passed.<br>\n";
}
Nested if statements
if (condition){ if(condition){
statements} else{
statements}
} else{statements
}
Other uses of if statements
if ($catGender=="Male" ){
$catPronoun = "He";
}elseif ($catGender=="Female" ) {
$catPronoun = "She";
} else {
$catPronoun = "The cat";
}
echo "I have a $catGender $catColour cat named $myCat. $catPronoun is $catAge years old."
If statements your turn
Write the PHP statements to – Take both a cat’s age in
years and a humans as input passed from a form
– Calculates the age of the cat in human years and displays it
– Displays a statement saying if the cat is older or younger than the person in cat equivalent years
Cat age calculation formula details
Year 1 = 15 human years
Year 2 = 9 human years
Years 3+ = 4 human years per year
Advanced topic:The switch statementswitch ($catGender){case "Male" :
$catPronoun = "He";break;
case "Female" : $catPronoun = "She"; break;
default : $catPronoun = "The cat";
}
PHP conditional statements summary• Used to control the flow of execution of
statements in a script• Based on the evaluation of a Boolean
statement through the use of comparative and logical operators
• Can use the if, elseif and else statements to compose more logically complex statements
• Can be nested within each other