ITC 240: Web Application Programming Subhash Prajapati 04/23/15

Review Array - variable type that can hold many values at a time Indexed Array - arrays with numeric index Associative Array - arrays with named keys Multidimentional Array - arrays within the array

Today Array Exercise Loops

Review Exercise: 6.1 Create students array that would include all the students name in a class [Numeric Indexed Array] Create a states array with state abbreviations as keys [Associative Array] Create students array with marks on different subjects [Multidimensional Array]

unset()/isset() These are two PHP built-in functions to do following: isset() - check whether a variable is set or not (od ) unset() – destroys the variable We can destroy/delete the array element like this: unset ($myArray[2])

Loop We can alter the flow of control using either conditionals or loops Loops: execute a statement(s) over and over. Usually contains: - a start condition - a break condition - change in each iteration

while loop loops through a block of code as long as the specified condition is true

while loop Syntax: while (condition) { // code block to be executed }

while loop example Following loop will iterate 4 times $counter = 1; while ($counter<5) { echo “The counter is: ” . $counter.”<br>”; $counter++; }

Quiz What happens to following code $counter = 0; while ($counter < 1) { echo “The counter is: ” . $counter.”<br>”; $counter--; }

Class Exercise 6.2 Write a program with while loop, which would print following table of squares (styling not required) Number Square Value 1 2 4 3 9 16 5 25 6 36 7 49 8 64 81 10 100

while loop alternative syntax while (expression): // statements goes here endwhile; eg: $i = 0; while ($i<10): echo $i; $i++;

do .. while loop loops through a block of code once, and then repeats the loop for specified condition is true

do .. while loop Syntax: do { // code block to be executed } while (condition);

do .. while loop do { do_work(); } while (condition); is equivalent to while (condition) { }

while vs do .. while loop The difference between do-while and while is that do-while evaluates its expression at the bottom of the loop instead of the top. Therefore, the statements within the do block are always executed at least once.

while example scenario Consider a program which writes some text in a file until file size becomes 5MB. We can use while loop in this scenario like this. while(IsFileSizeLessThan5MB()) { WriteMoreData (); }

do .. while example scenario Let's consider another scenario where we want to take an integer input from user until user has entered a positive number. In this case we will use a do-while loop like this. do { TakeInputFromUser(); } while ($input < 0);

Class Exercise 5.3 Cumulative Sum: write a method (function) with a while loop that computes the sum of first n positive integer. for eg: if you pass 5, it will give 15 (sum of 1+2+3+4+5) hints: Declare a function which will take one argument, the function will return the sum Inside the function, write a while loop which will iterate n number of time (n= number passed in that function) Inside the while loop, do the addition of the numbers