Final Exam, 3/16/2015 CIS330, Winter 2015

Transcription

1 Final Exam, 3/16/2015 CIS330, Winter 2015 You have 2 hours to complete this exam. You are not allowed to use any books, notes, calculators, or electronic devices. Feel free to separate pages, just make sure to write your name on each sheet if you do separate them (once per sheet is sufficient). Write your answers carefully and legibly. Partial answers are better than no answer. Feel free to skip around and go back to an earlier question later. When you are asked to write a program, writing comments is optional but you are expected to use good style and indent appropriately to make your code easier to follow. In programming questions, you can assume all necessary headers are included. There are a total of 100 points on this exam (there are a few optional extra credit questions which are additional and not listed in the summary table below). Good luck! And may your buffers never overflow! PAGE SCORE POSSIBLE

2 This page is intentionally left blank, feel free to use it (additional pages are also available at the end).

3 1.) Consider the following C program, stored in a file prog.c on a Unix system. 1: #include<stdio.h> 2: #include<string.h> 3: voidfunc(char*ptr){ 4: strcpy(ptr,"bye!"); 5: 6: 7: intmain(){ 8: chars[10]="hi!"; 9: func(s); 10: printf("%s\n",s); 11: return0; 12: (a) [1 pt] Assume you are in the bash shell. How would you compile this program using gcc to create an executable file named prog.exe? (b) [1 pt] What is the name of the format (acronym is acceptable) of the file prog.o created with the following command: gcc c oprog.oprog.c (c) [4 pts] Will the compilation succeed? If not, why? If it compiles successfully and you run the resulting executable, what is the output? (d) [4 pts] Suppose we replace the definition of func (lines 3 5) with the code below. Will the new code compile? If not, why? If yes, what would the resulting executable output? 3: voidfunc(char*ptr){ 4: ptr="oops!"; 5:

4 2.) Answer the following questions about the C language briefly (a sentence or two at most). (a) [1 pt] Is the following statement true or false: In C, data members of structs can be declared private. (b) [1 pt] How would you declare a pointer variable in C that can be assigned to point to any other type of variable (e.g., int, double, float, etc.)? (c) [3 pts] Declare a dynamically allocated one dimensional array of 20 float elements in C and initialize all values to (d) [4 pts] What error(s) do you see in the example below (describe briefly)? Propose fixes for the problem(s). What would be the return value of main in your fixed version? [extra 1pt: how would you check the return value of main on the bash command line?] /*file:p2.c*/ voidfoo(intx,inty){ returnx>y?x:y; intmain(){ inta,b=1; returnfoo(a,b);

5 3.) [10 pts] Write a complete C program (you can omit headers) that implements a guessing game in which the user has 6 tries to guess a computer generated random number between 0 and 50. Recall that the C random number generator can be initialized with a call to srand(time(null)) and subsequent calls to rand() return pseudo random integer numbers between 0 and RAND_MAX. An example execution assuming the computer randomly picked 16 is shown below (if the user fails to guess the number, you should output an appropriate response). $./guessinggame Pleaseenteranumber(between0and50):25 Toohigh!Guessagain enteranumber:12 Toolow!Guessagain enteranumber:18 Toohigh!Guessagain enteranumber:15 Toolow!Guessagain enteranumber:16 Youguessedcorrectly! [Extra, optional, 2 pts: Write your implementation so it would compile with gcc, but not g++, and add a comment explaining why it is valid C but not valid C++ code.]

6 4.) Please specify the Unix or git command(s) for each task below (multiple correct answers are possible, just give one for each part). Assume bash is the command line shell. (a) [3 pts] What are the git commands to upload your local changes to the master repository (e.g., at bitbucket.org)? (b) [1 pt] Find the differences between the files foo.c and bar.c. (c) [1 pt] Get the full path for the current working directory. (d) [1 pt] Remove all object files in the current directory. (e) [1 pt] Check whether an executable named sticks.exe is running. (f) [1 pt] Get information on how to use the kill command. (g) [2 pts] Find a file named foo.c in any subdirectory starting from the current directory. [Extra credit 2pts: find the library libm.a in any directory on the machine.]

7 5.) Answer the following fill in the blank and true/false C++ questions. (a) [1 pt] A derived class inherits the of its base class. (b) [1 pt] In C++, the is the language construct primarily used to create objects. (c) [1 pt] The default access specification of class members is (choose one of public, protected, or private). (d) [1 pt] is when member functions in a class hierarchy behave differently depending upon which object performs the call. (e) [1 pt] A(n) class cannot be instantiated. (f) [1 pt] A(n) function has no body, or definition, in the class in which it is declared. (g) [1 pt] True or False: Protected members of a public base class become public members of the derived class. (h) [1 pt] True or False: Function arguments in C++ are always passed by value. (i) [1 pt] True or False: A class can have more than one constructor if each has different types or numbers of arguments. (k) [1 pt] True or False: In a multi threaded C++ application, all threads can read or write simultaneously to an object s data members. (Extra) [1 pt] variable acts as a gatekeeper to a section of code, allowing only a single thread in and blocking access to all others until the thread leaves the protected section of code.

8 6.) Each of the following C++ code fragments contains one or more errors. In each case, briefly describe the error(s) and suggest a fix (note that in most cases there are multiple possible fixes, you just have to suggest a single valid one). Assume all necessary headers have been included and usingnamespacestd; is specified. (a) [2 pts] //Originalcode: //Proposedfix(es): try{ throw3.1415; catch(stringe){ std::cout<<e; Error(s) description: (b) [3 pts] //Originalcode: map<string,int>m; m[4]="johndoe"; for(i=m.begin();i<m.end();i++) cout<<i.second<<endl; //Proposedfix(es): Error(s) description: (c) [5 pts] //Original(complete)C++code: structa{ intnum; public: A(inti):num(i); voidgetnum(){returnnum; ; classb:publica{ intdecrement(){return num; ; //Proposedfix(es): Error(s) description:

9 7.) Consider the C++ program below (assume all necessary includes) and a file test.txt with the contents (without quotes): Thisisproblemsix.Iwonderwhatitdoes. (a) [4 pts] Briefly describe what the program does. classfilestats{ (b) [4 pts] What will be printed to public: standard output? void readfile (stringname){ stringinput=""; stringpunct=".!?"; strings=""; intsum=0,count=0; ifstreamfile(name); while(file>>s){ input+=""+s; (c) [2 pts] What will be the contents if(punct.find(s[s.length() 1]) of the test.txt.stats file?!=string::npos){ sum+=input.length(); count++; input=""; file.close(); stats=pair<int,float>(count,(float)sum/count); void writestats (stringname){ ofstreamfile(name, ofstream::out); if(file.is_open()){ file<<stats.first<<endl<<stats.second<<endl; file.close(); pair<int,float> getstats (){ returnstats; private: pair<int,float>stats; ; int main (){ FileStatsfs; fs.readfile("test.txt"); cout<<"stats:" <<fs.getstats().first<<"," <<fs.getstats().second<<endl; fs.writestats("test.txt.stats"); return0;

10 8.) Answer the following C++ code questions. (a) [5 pts] Consider the complete program below. //File:p8.cpp #include<string> #include<algorithm> #include<iostream> intmain(intargc,char*argv[]){ std::stringtext=argv[1],newtext=text; intd='a' 'a'; std::transform(text.begin(),text.end(),newtext.begin(), [&](charch) >char{ if(ch>='a'&&ch<='z')returnch+d; elsereturnch; ); std::cout<<newtext<<std::endl; What does the program do? What will the output be if after compiling the code into the p8 executable, you run./p8 "duck!" (b) [5 pts] Write a C++ code fragment that uses a map to store data about course enrollment. Each map entry is a pair of the course (string) and a vector of 4 character student ID strings. Initialize the map with the following data: CIS330, [5324, 1124, 1251, 1215]; CIS315, [1124, 1251, 2115].

11 9.) [20 pts] Write a C++ (command line) application that classifies songs by mood. When the application is executed, it reads songs from a file and then iterates through each song, prompting the user to input his or her mood(s) that would best match the current song. Define the acceptable mood tags, e.g., happy, calm, active, sad, stressed, etc. (feel free to extend or replace with your own ideas). Multiple moods from among this set can be specified for each song. The user can also stop at any point by typing quit instead of specifying a mood list. After the user inputs moods for all songs or types quit, the songs are output together with their mood information in a new file. Example partial input file (each line contains Artist: Song): Everlast: Whatit slike ImagineDragons: Polaroid Jem: Amazing... Example partial output file (each line contains Artist: Song; moodlist ): Everlast: Whatit slike; sad, active ImagineDragons: Polaroid; stressed, happy, active Jem: Amazing; happy... Example execution (you can have more or different prompts):./moodymusic WelcometoMoodyMusic! Pleaseenteryourmoods(comma separatedlist) thatbestmatcheachsong. Validmoodchoicesare: happy, calm, active, sad, stressed Everlast: Whatit slike> sad, active ImagineDragons: Polaroid> unpleasant Sorry, unpleasantisnotavalidmood, pleasetryagain. ImagineDragons: Polaroid> stressed, happy, active Jem: Amazing> quit Thankyou! Yourmoodswerestoredinmymoodymusic.txt. Do not implement the full application in a single large main() function, but rather define appropriate classes and member functions, for example Song and MusicLibrary classes, but the ultimate choice of classes and functions is left to you. Extra points will be given for good use of C++ standard containers and algorithms.

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