Computer Science 100 Class Lab

CS100 Lab 5 – Practice Lab 1 In this lab you will write several programs to practice your basic Python skills. The first three activities are simple programming exercises, the programs in the last two activities do some image manipulation. Remember to never start with a blank screen. Copy a program you wrote for a previous lab and modify it. Activity 1: Random Test (2 points) I said that Python’s randint() function returns a random value inside a given range. For example, randint(1,100) will return a random value between 1 and 100. Let’s test the assertion that randint() returns a random number by writing a program that calls randint() a number of times and calculates the average value returned. If randint() is random, you would expect the average to be close to the middle of the range. In the example above, I would expect the average value to be close to 50. Write a program that calls randint(1,100) 10,000 times and returns the average. Once you have the program written, experiment a little bit. Try different ranges and change the number of times that you call randint(). Name the file that contains your program lab5-act1.py. Activity 2: Dice (3 points) In this activity let’s write a program that uses randint() to simulate tossing a 6 sided die. The number returned by randint() is not only random, but in addition to being random it is also uniform, which means any value is equally as likely to be returned (to put this in another way the dice are not loaded). Start with the program you wrote in activity one, and change it so the range for randint() is one to six. Now run the program so that randint() is called 10,000 times, simulating tossing a die 10,000 times. The output from your program should be around three. Now modify the program so that in addition to calculating the average, it counts the number of times a one is rolled, a two is rolled, a three is rolled, and so on. When the program is finished “rolling” the die, print out the average and the number of times each number was rolled. If randint() is uniform each number should have been rolled about the same number of times. Here is an important thing to keep in mind about randint(). Remember that every time you call randint() it will return a random number. So you only want to roll the die once each time through the loop, so randint() should only be called once each time through the loop. When you call randint() in your loop, you should save the value that is returned so that you can refer to it as many times as you need to in the loop. Think variable ���� Name the file that contains your program lab5-act2.py. Activity 3: Fibonacci Numbers (10 points) You have probably seen the Fibonacci sequence before. Here are the first few terms in the sequence: 1, 1, 2, 3, 5, 8, 13, 21, 34, … The first two terms in the sequence are 1 and then 1. After that, each term is the sum of the preceding two terms. In the example above, the next term in the sequence would be 55 (which is 21+34). More formally, F0 = 1 F1 = 1 FN = FN-2 + FN-1 In this activity you will write a Python program that prints out the first 20 terms in the Fibonacci sequence. The main part of this program will consist of a loop that prints out the sum of the preceding two terms in the sequence: for i in range(????): sum = sum of the last two terms print(sum) Somehow you will need to remember what the last two terms were. I sure hope you are thinking, not variable again ���� Hint: look at the formal definition. The only other thing you will need to do is to get things started, remember the first two terms in the sequence are one. You will also have to figure out what range to use to get the first 20 terms. One last hint: do not try to print everything inside the loop. Name the file that contains your program lab5-act3.py. Activity 2: Brighten a Photo (15 points) You can blame this activity on my decision to binge watch NCIS. I am in season three of the show. At this point in the show the forensic technician Abby and Special Agent McGee, are always coming up with new algorithms to enhance images received from security cameras and satellites. Some of these algorithms are realistic, others are well, made for TV. One easy adjustment to an image that might help you make see what is in the image is to brighten it. Brightening an image is easy. You simply add a constant value to the red, green, and blue value of each pixel in the image. The larger the constant, the brighter the resulting image. Here is a picture I took one night in my backyard: You really cannot make out a lot in the picture. You can see the railing on my deck, and if you look hard enough you can see my shed in the upper right-hand corner of the photo. Applying the “brightening” algorithm I described above, using a constant of 100, results in the image below: In this image you can see that there were two deer in my yard that night. These were the criminals that were raiding my garden every night. If you brighten a picture too much, you get a washed-out image. Here is that same image but brightened by 200: Here almost all the details of the picture have been brightened to the point where you cannot see them. About the only thing you can see are the trees at the back of the yard, and if you look hard you can start to make out the houses on the other side of my yard. For this activity, write a program that will brighten an image. Start with one of the programs you wrote in the previous two labs (the gray scale program might be a good starting point). The only trick to this program is remember that a color value cannot be greater than 255 (8-bit color remember?). After you brighten the color values for a pixel, before putting the new colors in the image, check to see if any color value exceeds 255. If a value exceeds 255, set that value to 255 since that is the maximum possible RGB value. If you read these words carefully you should be able to see exactly what you need to do in your program ���� Note that you can darken images as well. To darken you subtract a constant value from each color in the pixels. Here you need to make sure none of the resulting colors are negative, if they are you would set them to zero. I tell you this only if you happen to find yourself working in a crime lab and need to darken an image for the “boss!!” Name the file that contains your program lab5-act4.py.