Final Exam, 3/17/2016 CIS330, Winter 2016

Transcription

1 Final Exam, 3/17/2016 CIS330, Winter 2016 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! May the for be with you! PAGE SCORE POSSIBLE

2 1.) Consider the following C program, stored in a file prog.c. 1#include<stdio.h> 2#include<string.h> 3#include<stdlib.h> 4 5structMyStruct{ 6 char*foo; 7; 8 9voidfunc(structMyStructs){ 10 strcpy(s.foo,"bye!"); intmain(){ 14 structmystructa; 15 a.foo=(char*)malloc(10*sizeof(char)); 16 strcpy(a.foo,"hi!"); 17 func(a); 18 printf("%s\n",a.foo); 19 return0; 20 (a) [2 pts] Show the complete command(s) for compiling and linking this program into an executable called prog.exe: gcc o prog.exe prog.c (b) [4 pts] Will the compilation succeed? If not, why? If it compiles successfully and you run the resulting executable, what is the output? Yes, it will compile. The output is Bye!. (c) [4 pts] Suppose we replace the statement on line 16 "strcpy(a.foo,"hi!");" with the code below. Will the new code compile? If not, why? If yes, what would happen when you run the program? 16 a.foo="testing"; Yes, it will compile, but will likely crash when you run it because the strcpy will attempt to overwrite the static memory where Testing is stored. 1

3 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, memory allocated with malloc will be automatically freed upon returning from the function where malloc was called. False (b) [2 pt] Write a union data structure declaration that can contain either an int or a char. Show how you would use it to declare a variable. union Data{inti;charc;myVar; Or union Data{inti;charc;; union DatamyVar; (c) [5 pts] Write a short C function foo that takes as arguments a 2 D array of integers and returns a 1 D array containing the sums of each row of the 2 D array s elements. For example, if you call foo with the two array arguments and provide an array containing as the first argument, the second array argument should contain [4, 10] when the function returns. voidfoo(int**a1,int**a2,intm,intn){ if(*a2==null) *a2=(int*)malloc(m*sizeof(int)); for(inti=0;i<m;i++){ (*a2)[i]=0; for(intj=0;j<n;j++) (*a2)[i]+=a1[i][j]; (d) [2 pts] What is a valid type for the variable myvar? Write the complete declaration for myvar and then give it some valid initial value. strcpy(myvar,"helloworld!"); Two possible answers, other valid answers exist: charmyvar[30]; or char*myvar=null; strcpy(&myvar, "" ); myvar=(char*)malloc(30); 2

4 3.) [10 pts] Write a complete C program (you can omit #include directives for headers) that computes the maximum from a space separated list of integer values (you can assume they are all positive). Recall that scanf( %d,&v) reads in an integer value from standard input. In addition to the main() program, create a separate function for finding the maximum value with the following function prototype: intfind_max(int*arr,intn) An example execution is shown below. Provide some basic input checking to handle wrong inputs without crashing. $./maximizer Pleaseenterthenumberofelements(between1and10,inclusive):10 Pleaseenter10numbersseparatedbyspaces: Themaximumis31. [Extra, optional, 1 pt: 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.] #include<stdio.h> #include<stdlib.h> intfind_max(int*arr, intn){ intmax= 1; for(inti=0; i<n; i++) if(arr[i] >max) max=arr[i]; returnmax; intmain(){ inti,n= 1,n_entered=0,*values=NULL; while(n<1 n>10){ printf("pleaseenterthenumberofelements(between1and10, inclusive):"); scanf("%d",&n); values=(int*)malloc(n*sizeof(int)); while(n_entered!=n){ printf("pleaseenter10numbersseparatedbyspaces:"); for(i=0; i<n; i++){ scanf("%d",&values[i]); n_entered=i; printf("themaximumis%d.\n", find_max(values,n)); return0; 3

5 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)? gitcommit m Someinformativemessage. gitpull gitpush #doamergecommitfirstifneeded (b) [1 pt] Find out when a file foo.c was last modified. ls lfilename,statfilename,... (c) [1 pt] Show all environment variables. env,printenv (d) [1 pt] Remove a directory and all its contents. rm rdirname (e) [2 pt] Check how long a process (e.g., vim ) has been running and how much memory it is using. [Extra credit 1pt: kill that process with the signal most likely to really kill the process.] ps a grepvim (f) [1 pt] Get information on how to use the top command. mantop,infotop,top help,... (g) [2 pts] Return the count for all occurrences of the string Moo in the file foo.c (Hint: use two commands separated by ). grep Moo foo.c wc l 4

6 5.) Answer the following fill in the blank and true/false C++ questions. (a) [1 pt] A derived class inherits all public and protected data members of its base class. (b) [1 pt] In C++, memory for pointer variables can be allocated by using the new operator. (c) [1 pt] The default access specification of class members is _ private (choose one of public, protected, or private). (d) [2 pt] An _ overloaded operator such as +,, etc. operator is a function that defines new behavior for an (e) [1 pt] The private data and function members of a class cannot be accessed by derived classes. (f) [1 pt] A(n) pure virtual function has no body, or definition, in the class in which it is declared. (g) [1 pt] True or False: Function arguments in C++ are always passed by reference. False (h) [1 pt] True or False: In C++, pure virtual functions have no implementations. True (i) [1 pt] True or False: A class can have more than one function with the same name if each has different types or numbers of arguments. True (Extra) [1 pt] What kind of pointer type (provided in the C++ standard library) can be used to automatically track the number of references to a given memory location? shared_ptr 5

7 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 per error). Assume all necessary headers have been included and usingnamespacestd; is specified. (a) [2 pts] //Originalcodefragment: voida::a{ i=3;//iisanintdatamemberofa //Proposedfix(es): A::A(){ Error(s) description: 1. Constructor returning value, 2. Constructor function missing (). (b) [3 pts] //Originalcodefragment: vector<string>v; v[0]="welcome"; for(i=0;i<v.size();i++) cout<<v[i]<<endl; //Proposedfix(es): v.push_back( Welcome ); for(inti=... Error(s) description: 1. The variable i has no type; 2. Because we didn t specify a size, to add elements, use push_back. (c) [5 pts] //Original(complete)C++code: //Proposedfix(es): classa{ classa{ intnum; public: A(inti){i=num; intnum; ; A(inti){num=i; classb:publica{ ; intiseven(){returnnum%2==0; ; Error(s) description: 1. i=num should be num = i; 2. Constructor is private; 3. Num should be public if B accesses it. 6

8 7.) Consider the C++ program below (assume all necessary includes) and a file test.txt with the contents (only the text between the quotes): In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move. Douglas Adams s Hitchikers Guide to the Galaxy (a) [4 pts] Briefly describe what the program does, i.e., what it computes. The program reads words (space separated) from a file, counts the number of words and finds the average number of characters per word. It also counts the number of sentences. It outputs the number of sentences, followed by number of words, followed by the average number of characters per word. classfilestats{ (b) [4 pts] What will be printed to public: standard output? void func1 (constchar*name){ stringw=""; stringpunct=".!?"; Stats: ints=0,c1=0,c2=0; ifstreamfile(name); while(file>>w){// readaword s+=w.length();c1++; (c) [1 pt] What is the type of the if(punct.find(w[w.length() 1]) st variable in main?!=string::npos){ c2++; _ vector<int> file.close(); stats.push_back(c2); (d) [1 pt] What would this program stats.push_back(c1); output if the file test.txt stats.push_back(s/c1); contained just "." (without the quotes)? vector<int> getstats (){returnstats; private: Stats: vector<int>stats; ; int main (){ FileStatsfs; fs.func1("test.txt"); cout<<"stats:"; autost=fs.getstats(); for_each(st.begin(),st.end(),[](inti){cout<<i<<"";); cout<<endl; return0; 7

9 8.) Answer the following C++ code questions. (a) [6 pts] Consider the complete program below. //File:p8.cpp #include<string> #include<algorithm> #include<iostream> #include<vector> intmain(intargc,char*argv[]){ intn=stoi(argv[1])+1; if(n<=0)return0; vector<int>v; for(inti=0;i<n;i++) v.push_back(i); intm=count_if(v.begin(),v.end(), [](inti) >bool {return((i%2)==1); ); std::cout<<"result:"<<m<<endl; return0; What does the program do? The program converts the first command line argument to an int, Initializes a vector with values from 0 to n 1, then counts the number of odd values in that vector and outputs the result. What will the output be if after compiling the code into the p8 executable, you run "./p85 "? Result: 3 (b) [4 pts] Write a C++ code fragment for a data structure that can be used to store a collection of 2 D coordinates. Initialize the data structure you declared with the following data: (0,0), (2,1), (5,3). vector<pair<int,int>>coords; coords.push_back(pair<int,int>(0,0)); coords.push_back(pair<int,int>(2,1)); coords.push_back(pair<int,int>(5,3)); 8

10 9.) [20 pts] Write a C or C++ implementation of the game Tic Tac Toe. Game description: Two players, X and O, take turns marking the spaces in a 3 3 grid. The player who succeeds in placing three of their marks in a horizontal, vertical, or diagonal row wins the game. Below is an example progression of the game where player X wins at the end. Implement a two player version of the game. For each player s turn, that player enters the coordinates of their next move, e.g., 1,1 puts your mark in the top left space of the board, and 3,1 puts your mark in the bottom left space of the board. Do not implement the full application in a single large main() function, but rather define appropriate classes and member functions (if using C++) or functions (if using C). Extra points will be given for good use of C++ standard containers and algorithms. Extra credit (up to 5 points): Implement a human vs computer mode. Partial sample output from an example execution where player O wins at the end (you can format your I/O differently if you wish!):./tictactoe WelcometoTicTacToe! _ _ _ _ PlayerX>2,2 _ _ X _ PlayerO>1,1 O _ X _ PlayerX>3,1 O _ X _ X PlayerO>1,3 O _ O _ X _ X... O O O _ X _ X X PlayerOwins! 9

11 #include<iostream> #include<string> usingnamespacestd; classgame{ public: Game(){ board=string(9,'_'); players[0] ='X'; players[1] ='O'; playerindex=0; nummoves=0; voiddisplay(){ for(inti=0; i<3; i++){ for(intj=0; j<3; j++){ cout<<board[i*3+j]; if(j<2) cout<<' '; cout<<endl; voidreset(){ board=string(9,'_'); nummoves=0; playerindex=0; charcheckwinner(introw, intcol){ charwinner='.'; for(intk=0; k<2; k++){ if((board[0]!='_'&& board[0] ==board[4]&& board[0] ==board[8]) (board[2]!='_'&& board[2] ==board[4]&& board[2] ==board[6])){ // Diagonals winner=board[0]; else{ for(inti=0; i<3; i++){ if(board[i*3] =='_' board[i] =='_') continue; if(board[i*3] ==board[i*3+1]&& board[i*3] ==board[i*3+2]){ //Rows winner=board[i*3]; break; elseif(board[i] ==board[i+3]&& board[i] ==board[i+6]){ //Columns winner=board[i]; break; //fori 10

12 //fork returnwinner; boolmove(){ introw= 1, col= 1; booltaken=false; charwinner='.'; do{ if(taken) cout<<"thatspotisalreadytaken, tryagain!" <<endl; cout<<"player" <<players[playerindex] <<" >"; cin>>row>>col; if(board[(row 1)*3+col 1]!='_') taken=true; else{ taken=false; board[(row 1)*3+col 1] =players[playerindex]; while(row<1 row>3 col<1 col>3 taken); if((winner=checkwinner(row,col))!='.'){ cout<<"gameover! Player" <<winner<<" wins!" <<endl; returnfalse; else{ nummoves++; if(nummoves==9){ cout<<"gameisatie!" <<endl; returnfalse; playerindex=(playerindex+ 1)% 2; returntrue; private: stringboard; charplayers[2]; intplayerindex; intnummoves; ; intmain(){ Gamegame; cout<<"welcometotictactoe!" <<endl; do{ game.display(); while(game.move()); return0; 11