Laboratory Exercise on For and While Loops, Part 1

For Loops

1. Consider the loop:

   for($i = 6; $i <= 12; $i++){
   	echo $i
        }
      

   1. Where does this for loop begin?
   2. When does this for loop end?
   3. What does this for loop print out?

2. Next, consdier this loop

    for($i = 20; $i <= 10; $i--){
   	echo $i;
   	}
      

   1. Where does this for loop begin?
   2. When does this for loop end?
   3. What does this for loop print out?

3. What does this for loop print out?

   	for($i = 1; $i <= 50; $i ++){
   		$i = $i*2;
   		echo $i;
   	}
      

4. Using a for loop, print out numbers 1 through 10:

   1. Format the numbers so they appear on a single line with a space between each number.
   2. Format the numbers, so they appear on separate lines.
5. a) Initialize a constant, doubleIt, outside of the for loop and set it equal to 1. Within the for loop multiply doubleIt by 2, and print out each multiple 10 times.
   b) Now print each item in a new line.

6. A Table of Fahrenheit and Celsius Temperatures

   Given a temperature in Fahrenheit, the equivalent temperature in Celsius is given by the formula:

   Celsius = (Fahrenheit - 32) * 5.0 / 9.0
     

   Write a program that shows the Celsius temperatures corresponding to Fahrenheit temperatures 50, 51, 52, ..., 70. For example, possible output might have the form:

   Fahrenheit   Celsius
       50        10.0
       51        10.6
       52        11.1
       53        11.7
       54        12.2
       55        12.8
       56        13.3
       57        13.9
       ...       ...
     

7. Interest in a Savings Account

   A simple savings account earns compound interest over time, based upon an annual interest rate (e.g., 1% or 9%) per year. The basic computations proceed as follows:

   • A monthly interest rate is computed:

     monthlyRate = annRate / 1200.0;
         

   • The monthly rate determines the interest the bank adds to the account each month, according to the formula:

     interest = monthlyRate * (old balance)
     new balance = (old balance) + interest
         

     For example, at an annual rate of 8%, the monthly rate is 0.00666667. With a starting balance of $100, the computations proceed as follows for the first year:

            Starting   Monthly   Ending
     Month   Balance   Interest  Balance
       0      ------     ----     100.00
       1      100.00     0.67     100.67
       2      100.67     0.67     101.34
       3      101.34     0.68     102.01
       4      102.01     0.68     102.69
       5      102.69     0.68     103.38
       6      103.38     0.69     104.07
       7      104.07     0.69     104.76
       8      104.76     0.70     105.46
       9      105.46     0.70     106.16
      10      106.16     0.71     106.87
      11      106.87     0.71     107.58
      12      107.58     0.72     108.30
         

     1. Write a program that produces this table of monthly balances, for an initial balance of $100 and an annual rate of 8%.
     2. Refine the original program, so that the initial balance and annual rate are supplied by a user form.

While Loops

8. What is printed by the following loop?

    
   	$x = 4
   	while($x <= 10){
   		echo $x;
   		$x ++;
   	}
     

   • Explain where does this while loop begin.
   • When does this while loop end?

9. What does this while loop print out?

    
   	$x = 5;
   	while(x != 0){
   		echo $x;
   		$x--;
   	}
      

10. Write a while loop that prints out numbers from 13 to 26.

11. Write code utilizing the following outline:

    • Initialize a variable called $x and set it equal to 1.
    • Using a while loop, let the condition be that $x is less than 1000.
    • Within the while loop
      • Print out $x.
      • Then multiply $x by 5.

    Explain in words what this program does.

12. Write code with the following steps that uses while loop to count down from 10 to 0, printing each item on a new line. After the count down is complete, the code should print "done".

Determining Whether to Use a For loop or a While loop

For the following questions, state whether you should use a for loop or a while loop. Then explain why you chose to use that loop.

13. Task: Loop through all odd numbers from 1 to 100.

14. Terminology: An integer $i is said to be divisible by the integer $d, if division of $i by $d yields no remainder. (In terms of PHP, $i % $d = 0 (recall % is PHP's symbol for finding a remainer.)

    Prime numbers: A number $i is said to be prime, if $i is divisible only by 1 and itself. (That is, $i is not divisible by any integers 2, ..., $i-1.)

    Task: Given an integer $i, determine whether or not it is prime.

created 24 January 2019 by Saniya Lakka revised 26-31 January 2019