Exercise : a,
b, and c
What are the values of a, b, and c
after the following statements? Write your answers in the boxes on the
right.
int a = 5; int b = 10; int c = b; a = a + 1; // a? 6 b = b - 1; // b? 9 c = c + a; // c? 16
Exercise : simple for loop
- Copy/paste the following code into jGRASP.
public class Count2 { public static void main(String[] args) { for ( fill me in! ) { System.out.println( fill me in! ); } } } - Modify the code to produce the following output:
2 times 1 = 2 2 times 2 = 4 2 times 3 = 6 2 times 4 = 8
Exercise : Verify solution in Practice-It!
Our Practice-It! system lets you solve Java problems online.
-
Go to the
Practice-It!
web site.
- Create an account if you don't have one, and log in.
- Under the "CS1 Labs", "Lab 2" category, select the "simple for loop" problem. (direct link)
- Copy/paste your program from jGRASP into Practice-It, and submit. If it does not pass the test, modify your code and re-submit it.
Exercise : What's the output?
What output is produced by the following Java program? Write the output in the box on the right side.
public class OddStuff {
public static void main(String[] args) {
int number = 32;
for (int count = 1; count <= number; count++) {
System.out.println(number);
number = number / 2;
}
}
}
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Output: 32 16 8 4 |
Exercise : jGRASP Debugger
-
Breakpoints help you debug programs (tutorial). Copy/paste this code into jGRASP:
1 2 3 4 5 6 7 8 9 10
public class Numbers { public static void main(String[] args) { int number = 42; for (int i = 1; i <= 1000; i++) { number = number * 37 % 103; } int number2 = number * number; System.out.println("result = " + number2); } } -
Set a breakpoint on the statement inside the
forloop (line 5). Do this by moving your cursor to the beginning of that line until you see a stop-sign icon
and then clicking.
continued on the next slide...
Exercise - jGRASP Debugger
-
Now you can debug the program by clicking on the debug icon
(looks like a ladybug).
-
It will stop every time it hits line 5.
Then you can see the values of variables
iandnumber. -
To continue running, press the top-left play
or step
buttons.
-
Using this approach, fill in the table below indicating what value
numberhas whenihas the given value. Keep in mind that you are figuring out what valuenumberhas just before it executes this line of code.i = 1, number =42
i = 2, number =9
i = 3, number =24
i = 4, number =64
continued on the next slide...
Exercise - jGRASP Debugger
-
Click on the stop-sign
a second time to get rid of it and then set a new stop point on line number 7.
This will allow you to find out the value of
numberafter the loop is done executing. -
Again press "play"
to start the programming running again.
-
At line 7, what is the value of
number? 69
Exercise : printing a design
Write a program to produce the following output using nested for loops. Use a table to help you figure out the patterns of characters on each line.
-----1----- ----333---- ---55555--- --7777777-- -999999999- |
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Test your loop expressions in Practice-It! using the checkmark icon above. Use your expressions in the loop tests of the inner loops of your code.
Exercise : SlashFigure
Write a Java program in a class named SlashFigure to produce the following output with nested for loops. Use a loop table if necessary to figure out the expressions.
!!!!!!!!!!!!!!!!!!!!!! \\!!!!!!!!!!!!!!!!!!// \\\\!!!!!!!!!!!!!!//// \\\\\\!!!!!!!!!!////// \\\\\\\\!!!!!!//////// \\\\\\\\\\!!////////// |
|
Test your code in Practice-It! or the Output Comparison Tool.
Exercise : Parameter Mystery
-
Fill in the boxes with the output that each method call would produce:
public class MysterySoda { public static void main(String[] args) { String soda = "coke"; String pop = "pepsi"; String coke = "pop"; String pepsi = "soda"; String say = pop; carbonated(soda, pop, pepsi); // say pepsi not soda or coke carbonated(coke, soda, pop); // say coke not pepsi or pop carbonated(pop, pepsi, pepsi); // say soda not soda or pepsi carbonated("pop", pop, "koolaid"); // say pepsi not koolaid or pop carbonated(say, "say", pop); // say say not pepsi or pepsi } public static void carbonated(String coke, String soda, String pop) { System.out.println("say " + soda + " not " + pop + " or " + coke); } }
Exercise : Parameter Mystery
-
Fill in the boxes with the output that each method call would produce:
public class MysteryNumbers { public static void main(String[] args) { String one = "two"; String two = "three"; String three = "1"; int number = 20; sentence(one, two, 3); // three times two = 6 sentence(two, three, 14); // 1 times three = 28 sentence(three, three, number + 1); // 1 times 1 = 42 sentence(three, two, 1); // three times 1 = 2 sentence("eight", three, number / 2); // 1 times eight = 20 } public static void sentence(String three, String one, int number) { System.out.println(one + " times " + three + " = " + (number * 2)); } }
Exercise : printNumbers
-
Write a method
printNumbersthat accepts a maximum number as a parameter and prints each number from 1 up to that maximum, inclusive, boxed by square brackets. For example, the following calls:printNumbers(15); printNumbers(5);should produce the following output:[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [1] [2] [3] [4] [5] - You may assume that the value passed to printNumbers is 1 or greater. Check your answer using Practice-It from the check-mark icon above.
Exercise : printSquare
-
Write a method
printSquarethat accepts min and max integers and prints a square of lines of increasing numbers. The first line should start with the minimum; each line that follows should start with the next-higher number. The numbers on a line wrap back to the minimum after it hits the maximum. For example, the call:printSquare(3, 6);should produce the following output:3456 4563 5634 6345 - If the maximum passed is less than the minimum, the method produces no output. Check your answer using Practice-It from the check-mark icon above.
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Hint 1: remember the mod operator...
Hint 2: The mod solution can be tricky, instead try 2 inner loops rather than 1...