CS 151

Assignments

[Note: this webpage last modified Monday, 29-Apr-2013 23:23:22 EDT]

Final exam

See review.html for a review of many of the things we know about C.
The topics for the final are ...
- Everything we've done in C (but not structures).
- You should understand all the homeworks, quiz and practice quiz questions, and previous exam questions.
- Practice the practice questions listed in the notes.
- Things you may want to memorize:
  - Doing something BLANK times with a for loop. E.g., 5 little ducks or 100 bottles of liquid.
  - Doing something to each thing in an array using a for loop. E.g., add one to each item in the array, or count how many are even.
  - Reading from a file. Writing to a file.
  - Ask the user for something until BLANK (e.g., until they guess your number, or enter the correct password.)
  - Making a function that asks the user for a bunch of numbers and returns the total. Then use that in main to do something.
  - Function to swap two variables and then use it in main.
  - Take a number and print out the letter grade.
  - [Check back later for more, maybe.]
- NOT on the exam: assembly language, Scratch.
Exam format will be the same as the first two exams.
Practice questions... Not right now, just practice the practice question!!

Some sample questions - be the computer ...

...
char s[100] = "hi"; int i;
for(i=0;i<3;i++) printf("%d\n", s[i]);

...
int nums[5] = {5, 4, 3, 2, 1};
int i;
for(i=4; i>=0; i--) {
  printf("%d\n", nums[i]);
  i = i / 2;
}

...
int x, y, *z;
x = y = 1;
z = &x;
*z += 1;
y = *z * x;
printf("%d, %d, %d\n", x, y, *z);

...
char s[100]="hi", *ch;
ch = s;
printf("%c, %c\n", ch[0], ch[1]);
printf("%d\n", ch == s);

...
char s[100] = "this is the song that ends.";
int i;
for(i=0;i<strlen(s);i++) {
 s[i] = s[i] - 1;
 if (s[i] == 'a'-1) s[i] = 'a';
 toupper(s[i]);
 //s[i] = toupper(s[i]);
 if (s[i] == ' ') i += 1;
}
printf("%s\n", s);

```
...
int *fun(int *x, int *y) {
  if (x == y) return y;
  else if (*x < *y) return x;
  return y;
}
int main(int argc, char *argv[]) {
  int i=2, j=3, x;
  x = *fun(&j,&i);
  printf("x = %d\n", x);
  return 0;
}
```
answer: well, you can run it to see what happens. fun takes two pointers as parameters and returns one of them. If the numbers they point to have the first one smaller, then the first pointer is returned. When this is called in main, the values are 3 and 2. 3 is not smaller than 2, so the second pointer is returned, which is &i. x is set to * of that address, meaning the value of i, which is 2. This means the print statement prints 2.

...
FILE *myFile = fopen("blah.txt", "w");
char s[100]="";
int i;
for(i=0;i<3;i++) {
  s[strlen(s)+1]  = '\0';
  s[strlen(s)] = 'a';
  fprintf(myFile, "%s\n", s);
}
fclose(myFile);
myFile = fopen("blah.txt", "r");
char ch = fgetc(myFile);
int count=0;
while (ch != EOF) {
  if (ch == '\n') count += 1;
  ch = fgetc(myFile);
}
fclose(myFile);
fprintf("count = %d\n", count);

answer: The first for loop prints the following into blah.txt

a
aa
aaa

The while loop then reads every character from blah.txt and counts the number of new line characters. There was one for each iteration of the for loop, so 3. That means count will be 3.

...
int f(int x, int y, int n) {
  int temp;
  for( ; n > 0; n--) {
    temp = y;
    y = x + y;
    x = temp;
  }
  return y;
}
int main(int argc, char *argv[]) {
  int i = f(0,1,3);
  i = f(i,i,3);
  printf("%d\n", i);
  return 0;
}

Project

Rules.

Can work with a partner or alone. Only groups of 2 are allowed, no groups of 3. Groups will be required to turn in something saying how much work each person did, and that will influence each person's grade.
Check in with me each week about what you need to do on your project that week. These will count for HW grades.
First checkin is this week - come talk to me about what you plan to do for your project. We'll come up with intermediate goals to work towards.
Final version of your code is due by May 4 (end of exam week).
You will give a ~ 5 minute presentation of your project during the last week of classes or exam week.
Final version of your code must use: multiple functions, multiple loops, user input/output, arrays, use of files.
You can pick from the ideas listed below. If you want more description about an idea, then ask. If you have some other idea you want to do, you have to get it approved by me first.

Project choices.

Encryption/decryption. Possibilities: Caesar/keyword/permutation cipher, Vigenere, scytale, playfair, AES, RSA.
Cryptanalysis. Breaking any of the preceding.
Ncurses game. Possibilities: snake/worm/centipede, asteroids/astrosmash, maze/adventure.
Equation grapher. Graph equations involving polynomials, sin, cos, tan, ...
Line drawings. Save a bunch of lines as a bitmap image.
Equation solver. Using Newton's method.
Eliza/doctor/chat-bot.
Web search/crawl.
Ncurses text editor.
Shell. Make your own shell, implement your own commands, login stuff, ...
Text search. Search a text file for (blank), count number of times (blank), ...
Ncurses planetary simulator.
Scratch game/project. Possibilities: ISU adventure, ISU tour/map, typing/spelling/math tutor/game, .
Computing digits of pi, e, or other numbers.
Prime numbers sieve.
Card games: poker, go fish, pokemon, ... .
Board games: monopoly, scrabble, chess, ... .
Factoring algorithms: trial division, ...
Typing tutor/game.
Spelling tutor/game.
Math/arthmetic tutor/game.

Second exam

Topics. The exam covers everything we have done so far in terms of C programming and algorithms.

Topics that were on the first exam that are NOT on this exam include: assembly language programming, converting between binary/decimal/hexadecimal. Shell commands (cp, mv, etc.) will not be tested per se (there won't be questions where you get points just for knowing how to use the shell/terminal), but you'll need to be able to do those things to do the programming parts on the computer.

Note that the schedule has on it a few things we have not done yet (file input/output, malloc/free, time/clock, struct, enum, typedef, union). Those will not be on this test.

Okay then. The areas you should focus on for the test are...

C programming syntax - know what every punctuation item is used for. E.g., () are used to group for order of operations, and when defining or calling a function.
C programming syntax - know what all the keywords we have used are for (e.g., int, float, char, for, while, if, do).
C programming basics - arithmetic and data types. Be able to do basic arithmetic and understand the basic data types (int, float, char, char []). Understand how strings work (a bunch of characters, with the last one being '\0' to indicate the end of the string). Understand that each character has a number code (the ASCII code) that you can print using printf.
C programming basics - input and output. Be able to use printf, scanf to get input or print integers, floats, characters, strings.
C programming ideas - loops. You should be able to do basic things with for loops and while loops.
C programming ideas - if statements and Boolean logic. You should be able to use if statements. That includes being able to come up with Boolean conditions for things. For example, to test if a number grade is a B, you'd do
```
if (grade >= 80 && grade < 90) { ...}
```
C programming ideas - functions. You should understand how functions are created and called. You should be able to make functions to do basic things.
C programming ideas - arrays, pointers, memory addresses. You should be able to declare and use arrays, and understand how pointers work.
Debugging. You should be able to take a program with syntax/runtime errors and fix them.
Algorithms. The following are some algorithms we've looked at that you should understand: finding smallest number in a an array, using loops to print lines/triangles/squares/etc., converting between different units (e.g., inches and centimeters), adding up all the numbers from 1 to something, swaping the values in variables, doing something BLANK times (for loop), doing something until BLANK (e.g., ask for password until they type the right thing), compute the total of an array of numbers, take an average of a bunch of numbers (either from an array or that was input from the user), determine the length of a string, compare two strings, print out all the evens or multiples of 3 or ..., print out all the perfect squares.
HW assignments, in-class code examples. For all the C programs we did on HW assignments or in class, you should understand how they work and be able to make changes to them.
Quiz questions and practice quiz questions. Those are good practice too.

Exam format. Same as the last time - half on paper, half on the computer.

Practice questions.

On paper. What is the final value printed by the following code? Show your work for the variables and functions.

  // #includes ...
  void okay(int num, int *x, int z[]) {
    int i, total=1;
    for(i=0; i<num; i++) {
      z[i] = total * (i+1);
      total = total * (i+1);
    }
    *x = z[num-1];
  }
  int main(int argc, char *argv[]) {
    int numbers[4] = {0, 0, 0, 0};
    int howMany = 4, result = 0;
    okay(howMany, &result, numbers);
    printf("%d, %d\n", result, numbers[0]);
  }

On paper. What is the final value printed by the following code? Show your work for the variables and functions.

  // #includes ...
  int smallestBiggerThan(int numbers[], int howMany, int what) {
    int smallSoFar = numbers[0];
    int i;
    for(i=0;i<howMany; i++) {
      if (numbers[i] < smallSoFar && numbers[i] > what)
        smallSoFar = numbers[i];
    }
    return smallSoFar;
  }
  int main(int argc, char *argv[]) {
    int nums[4] = {5, 3, 7, 2};
    int smallest = smallestBiggerThan(nums, 4, 0);
    int second = smallestBiggerThan(nums, 4, smallest);

    printf("%d and %d\n", smallest, second);
  }

On paper. Explain the difference between int and float.
On paper. Explain what a pointer is and what it is used for.
On paper. What is a buffer overflow?
On computer. Write a program that prints out the perfect cubes from 1 cubed up to 13 cubed.
On computer. Make a program that draws two triangles of stars, so they together form a bigger triangle - like
```
*
**
***
****
***
**
*
```
On computer. Fix the bugs in the program stored in exam2Practice1.c.
On computer. Fix the bugs in the program stored in exam2Practice2.c

First exam

Topics. The exam covers everything we have done so far. In particular, focus on the following as you study.

Shell commands: cp, ls, mv, rm, rmdir, cd, passwd, clear, mkdir. You should know what they do and how to use them.
Using the shell commands, just like we have been doing for hw assignments.
Binary, decimal, hexademical. You should be able to convert between all three of these.
Assembly. For our simple assembly language we used, you should be able to "execute" a simple program yourself on paper. So if I gave you a few assembly instructions, you should be able to say what each one does and what the final values are in memory and the registers.
Basic parts of a computer, how they work together. What are the differences between hard drive and memory? What does the CPU do?
C programming basics. Know all the rules we have talked about so far. This includes the rules for: printf, scanf, if, for, do while, variable declaration, function definition, calling a function, arthmetic, Boolean expressions, and all the punctuation that goes with each of these.
Basic C compiling and debugging. Be able to take a program that has some error when you compile it, and be able to read the error message and fix the error.
Basic C statements. Given a C program that doesn't do anything, be able to put in some simple statements (e.g., printf, basic arithmetic, single if test, ...).
HW assignments, in-class code examples. For the C programs and assembly programs we did in class or on HW assignments, you should understand the solutions.

Exam format. The exam will be in two parts - one on paper and one on the computer. Each of the practice questions is labeled as either on paper or on computer. For the on computer problems, you will have a terminal/putty, but there will be no internet access.

Practice questions.

On paper. Convert between decimal, binary, and hexadecimal. Use a calculator that has these choices or Wolfram alpha to test yourself. Examples...
Convert to binary: 99 decimal, FA hex.
Convert to decimal: 101011 binary, 8E7 hex.
Convert to binary: 156 decimal, 60B hex.
On paper. What is the largest number that can be represented with: 2 bytes, 2 hex digits, 4 decimal digits, 7 bits?

On paper. Given assembly code what does it do? Examples...

  setmem 98 5
  load 3 98
  add 3 3
  mult 3 3
  cpreg 1 3
  store 1 90
  print 90
  halt

  setmem 98 4
  load 1 98
  setmem 97 1
  load 2 97
  cpreg 3 1
  cpreg 4 1
  sub 4 2
  sub 4 3
  store 4 97
  print 97
  halt

On computer. Given assembly that is partially completed, complete it so it works correctly. Examples...

  // complete so the code adds up 11+13+17+19 and prints the result.
  store 99 11
  load 1 99
  store 99 13
  load 2 99
  store 99 17
  load 3 99
  store 99 19
  load 4 99
  add 1 2
  add 1 3
  // insert instruction to finish adding values...

  // insert two instructions to store and print the final answer.

On paper. Given some C code, what is the output and what happens to the variables. You would list the different values the variables had as the code ran, and would say what gets printed to the screen. Examples...

  // usual #include and int main stuff... inside of main is...
  int x = 3;
  int y = x * 5;
  int z;
  z = y + y;
  y = y - y;
  x = x / 10;
  printf("%d, %d, %d\n", z, y, x);

  // usual #include and int main stuff... inside of main is...
  float x, y, z;
  x = 3 / 6;
  y = x * x;
  z = x - y;
  if (z < y)
    printf("%d\n", z);
  else
    printf("%d\n", y);

On computer. Given some C code that has a variety of syntax errors, you should be able to fix them so it works correctly. Examples...

#include<stdio.h>
#include<stdlib.h>
int main(int argc, char *argv[]) {
  char choice
  printf("Even or odd?  Type E or O. ");
  scanf(%c, &choice);
  if (choice = 'E')
    printf("2 is even.\n");
  else
    printf('1 is odd.\n');
  return 0;
}

#include<stdio.h>
#include<stdlib.h>
float feetToMeters(float num) 
  float x;
  x = num*.914 \ 3.0;
  return x;

int main(int argc, char *argv[]) {
  printf("10 feet is %d meters.\n", feetToMeters 10);
  return 0;
}

On computer. Be able to use the shell/putty commands to do things. Examples...
Create a directory called examPractice in your home directory, and copy your hw5 solution there.
Go to the directory /net/web/dept. How many .html files are in that directory?
Copy the degrees.c file from the in class code. Put the copy in your examPractice directory, and make it named degreeCopy.c.
Go to the / directory. What directories do you see?
On paper. Questions showing basic understanding of how the computer works, what assembly language is, how programming works, etc. Examples...
List strengths and weaknesses of hard drives versus RAM memory.
What are the main steps in creating a program that one of your friends would be able to use?
On computer. Be able to take one of our examples from class and make some basic changes to it. Examples...
Take the degrees.c program, and make it so it prints the message "That's really cold" if the user enters a temperature less than 0 Celsius or 32 Fahrenheit.
Take the adding.151asm program and have it add up the numbers from -100 to 200.
Take the add.c program and make it test 30 through 39 for whether they are prime or not.

Software Environment/Installation/Login

Installing Scratch. We will have one or two assignments using a simple programming system called Scratch. Install it by going to Scratch Download.

Installing C. Either just use gcc by logging into the CS server using putty and your cs151xx account, or install a C compiler on your computer. If you use Linux or Mac, it is likely installed already. If you use Windows, you can install Cygwin.

It is absolutely required that you have access to a working computer with C installed (or a computer with Putty installed and an internet connection) that you have access to outside of class time. The biggest factor in your success in the course is how much time you spend programming outside of class.

Installing Putty and FileZilla. To install the FileZilla ftp client, go to FileZilla. To work on your assignments on the CS server, you must install Putty if you are using Windows. If you are using Linux or Mac, you can just use ssh from the terminal/shell.

cs151xx login to CS server. You will turn your assignments in by uploading your finished assignment to the Computer Science server. I have administrator access to this server and can easily grade your homeworks once they are on the server. You will receive an email giving you a username and login to the CS server. The username will be cs151xx, where xx is just a number - so the "first" student in the class will get cs15100 as their login, etc. You use either FileZilla or WinSCP with your CS login/password to upload your homework files to the CS server. This is demonstrated in the first lecture. That lecture has been recorded and is available to view in blackboard - go to blackboard for this course, and click "Tegrity Classes".

Emacs If you are programming by logging into the CS server or using Cygwin to edit your files, you have some choice about what text editor to use. Those installed on the CS server include: vi, pico, nano, emacs. If you want to use a strictly Windows text editor, you might try Notepad++. I use emacs because it does auto-indenting and other things. If you decide to use emacs, you'll need to learn the shortcuts for things. The ones I use most are the following (search online for others).

Save file: Ctrl-x Ctrl-s
Close emacs: Ctrl-x Ctrl-c
Undo: Ctrl-Shift-_
Auto-indent current line: Tab
Auto-indent current paragraph: Alt-q
Search forward in the file: Ctrl-s
Repeat last search: Ctrl-s Ctrl-s
Search reverse in the file: Ctrl-r
Delete character just right of cursor: Ctrl-d
Go to the end of the line: Ctrl-e
Go to end of file: Esc <
Go to begin of file: Esc >
Kill from cursor to end of line: Ctrl-k
Copy: Ctrl-spacebar to set beginning of copy region, then go to where you want the end of the copy region, then type Esc w.
Yank/paste what was just copy/killed: Ctrl-y
Cycle through yank buffer: after a Ctrl-y, type Esc y repeatedly to cycle through things that have been copy/killed.
Create new file or open existing one: Ctrl-x Ctrl-f
If more than one file is open, switch between them: Ctrl-x b
Close file but don't close emacs: Ctrl-x k
Switch to "split screen" mode: Ctrl-x 2
Switch windows in split screen mode: Ctrl-x o
Switch back to "normal screen" mode: Ctrl-x 1
Search/replace: Esc x replace-string
Open shell/terminal: Esc x shell
Spell-check (not used much on programming files, but anyway): Esc x ispell
View raw binary/hex data: Esc x hexl-mode.
Switch back to "normal" mode: Instead of hexl-mode, use one of the following depending on the type of file - c-mode, text-mode, html-mode.

Project

Basic idea: create a "significant" program that uses most of the key programming features we have learned in class. You can choose what the program does, but your choice must be approved by Jeff.

Rules:

May work alone or with one partner. If working together, you will include at each stage a description of what was done by each person.
Final code must use: well-chosen functions, loops, structures, user input and output, file input and output.

Homework Assignments

The homework assignments are posted in the in class code. hw1.c contains the first homework assignment, hw2.c is the second homework assignment, etc. I will announce in class and/or by email when a new assignment has been posted. Each homework assignment will list the date the assignment is due. Late assignments will not receive any credit; I will grade them just so you know how you did.

To complete a homework assignment, (1) download the assignment from the in class code, (2) make changes to the file provided to complete the assignement, (3) upload your completed assignment to the CS server before the due date. To download the file, you should browse to the in class code on the course website, right-click, and choose "Save as" or "Save target as" (depending on your browser) to save the file to your computer. For each assignment, you must download the template file to use as a starting point, make changes to this file, and then upload this file. If you do not turn in your homework in this way, I will take off points! DO NOT copy/paste into a word document, or send an email with your assignment. DO NOT change the name of the homework file - keep the name exactly the same as on the class website.

For each hw assignment, I will post a Tegrity video where I describe the hw assignment and show how my correct solution works. You will need to watch this video on your own time. The reason I do this is to FORCE you to spend some time outside of class looking at the homeworks.

CS 151 - Intro. to Programming - F2012

Contact

Assignments

Final exam

Project

Second exam

First exam

Software Environment/Installation/Login

Project

Homework Assignments