f11-exam2

ENGR 101: Intro to Computers & Programming -‐ Fall 2011 of 11

Exam 2 Fall 2011 Semester

Engr101: Introduction to Algorithms and Programming

Section 100 / 200 / 300

• You are allowed to use the books and your notes. • You may not use electronic devices: including, but not limited to, calculators, laptops, and cell phones. • You may not access the internet in any way. • You may not use any device that can interpret, compile, or run program code in any way.

• Write your uniqname on the top of each page of the exam (excluding the first page). • You are responsible for the legibility of your work. Any work that is not clear to the grader due to sloppiness

or poor handwriting will be marked incorrect. • You must read and sign the Honor Code below after you have completed the exam. Printed Uniqname: ___________________________ Printed Name: ____________________________

Circle your Lab Section below (you will lose 1 point if you don’t do this or it is incorrect): 101: Cat – Th, 8:30-‐10:30a 201: Lisa – Tu, 8:30-‐10:30a 301: Oz – Mon, 8:30-‐10:30a 102: Rob – Th, 10:30a-‐12:30p 202: Nader – Tu, 10:30a-‐12:30p 302: Oz – Mon, 10:30a-‐12:30p 103: Cat – Th, 12:30-‐2:30p 203: Apoorva – Tu, 12:30-‐2:30p 303: Jeff – Mon, 12:30-‐2:30p 104: Cassie – Th, 2:30-‐4:30p 204: Apoorva – Tu, 2:30p-‐4:30p 304: Sumit – Mon, 4:30p-‐6:30p 105: Rob – Th, 4:30-‐6:30p 205: Nader – Tu, 4:30p-‐6:30p 305: Oz – Wed, 8:30-‐10:30a 106: Cassie – Fri, 8:30-‐10:30a 206: Nader – Fri, 8:30-‐10:30a 306: Jeff – Wed, 10:30a-‐12:30p 107: Cassie – Fri, 10:30a-‐12:30p 207: Apoorva – Fri, 10:30a-‐12:30p 307: Jeff – Wed, 12:30-‐2:30p 108: Cat – Fri, 12:30-‐2:30p 208: Lisa – Fri, 12:30-‐2:30p 308: Sumit – Wed, 2:30-‐4:30p 109: Rob – Fri, 2:30-‐4:30p 209: Lisa – Fri, 2:30-‐4:30p 309: Sumit – Wed, 4:30p-‐6:30p

Number I II III IV V Total

Grade

I have neither given nor received aid on this examination, nor have I concealed a violation of the Honor Code.

Signature:_________________________

Uniqname: ____________________________


The remainder of this page is intentionally left blank.

Uniqname: ____________________________


Question 1 -‐ Matching (20 points)

Match each concept on the left-‐hand side with the phrase on the right that fits best. Note that there are more items in the right column than in the left, so some answers will not be used. _____ alias A. statement executed on each iteration _____ loop body B. extracts characters until next '\n' into string variable _____ member function C. keyword for defining generic routines _____ getline D. encloses condition in if or while statement _____ exit statement E. vector of vectors of generic types _____ local scope F. method associated with instances of a class _____ template G. alternate name declared using reference operator _____ floating point H. terminates program _____ () I. terminates function or procedure _____ ; J. marks end of simple statement

K. represent binary number in terms of mantissa, exponent, and sign

L. textual context for identifier introduced within

procedure or function

Uniqname: ____________________________


Question 2 -‐ Multiple Choice and Short Answer (20 points)

For parts a) through e) below, check the single most appropriate answer for each. a) Consider the predicate declaration: bool myPred(const vector<int> & theVector);

What is true about the input argument to this routine? (3 pts)

____ theVector cannot be modified within myPred ____ the variable passed as theVector cannot be modified within the caller ____ theVector has global scope ____ All of the above ____ None of the above b) Which of the following sorting algorithms prominently exploited recursion in lecture? (3 pts)

____ BubbleSort ____ InsertionSort ____ MergeSort ____ All of the above ____ None of the above c) Suppose that G is the greatest (most positive) value expressible in an integer representation, and L is the least (most negative) value. What is the result of evaluating the expression L-5 ? (3 pts)

____ G + 5 ____ G – 5 ____ G – 4 ____ L + 4 ____ None of the above d) Suppose we have declared s as an empty string. Which of the following prints GoBlue! on a single line of output? (3 pts) ____ s = "GoBlue!"; s[3]='l'; cout << s << endl; ____ s = "GoBlue!"; s.push_back('!'); cout << s << endl; ____ s = "GoBlue!"; cout << s[1] << "oBlue!" << endl; ____ s = "Blue!"; cout << s.append("Go") << endl; ____ None of the above

Uniqname: ____________________________


e) Consider the following iteration code, assuming i has been declared as an int: i=0; while (i+1 < 100) {

i++; cout << i;

} Which of the following for statements is equivalent? (3 pts)

____ for (i=0; i<99; i++) cout << i+1; ____ for (i=1; i<100; i++) cout << i; ____ for (i=1; i+1<=100; i++) cout << i; ____ All of the above ____ None of the above

f) Rank the following 8-bit two's complement numbers from 1 to 5, where the most negative number is labeled with a 1 and the most positive number is labeled with a 5. (5 pts)

____ 00000000 ____ 01010101 ____ 10101010 ____ 11111111 ____ 01100000

Uniqname: ____________________________


Answer:

Answer:

Question 3 – What does the code do? (20 points) In the space provided beside each of the following four programs, write one of the following:

• The screen output of the program, using underscore to denote any spaces (e.g. 6_24_42) • “Won’t finish” if the program would enter an infinite loop or potentially crash or otherwise fail to

terminate normally. Assume that each code has all necessary libraries included, and using namespace std; at the beginning. Do not put any “scratch work” in the answer box. int main() { ofstream a("zzzzz"); a << 1.2 << " 3.4 " << endl; a.close(); ifstream b("zzzzz"); while(not b.fail()) { double a; b >> a; cout << a << endl; } return 0; } int main() { string s = "November_2"; string s1 = "dissect?"; int j=5, k=6; for (int i=2; i<s.size(); i=i+4) { s1.at(j) = s.at(i); s1.at(k) = s.at(i+1); j--;

k++; } cout << s1 << endl; return 0; }

Uniqname: ____________________________


Answer:

Answer:

int main() { vector<int> v(6,1); for (int i=0; i<v.size(); i++) { v.at(i) = v.at(i) + v.at(i-1); cout << v.at(i) << " "; } cout << endl; return 0; } void s2(string s) { if (s.size()>2) { s2(s.substr(1,s.size()-2)); cout << s[0] << s[s.size()-1]; } else {

cout << s; } return; } int main() { string s = "November_2"; s2(s); cout << endl; return 0; }

Uniqname: ____________________________


Question 4 – Write some code (20 points) For this question, you must write the complete definition of a procedure, called flipflops, on the following page that takes a single string composed entirely of lowercase letters of any length, determines if the string flipflops, and finds the lowest and highest letters in the string if it does. A string of lowercase letters is said to flipflop if each character in the string is alternately higher in the alphabet or lower in the alphabet than the character before it. The first character in the string must always be lower than the second, the second must be higher than the third, the third must be lower than the fourth, etc. An empty string does not flipflop and a string with one character always flipflops. An example of a string that flipflops would be “abate” since the first ‘a’ is lower than ‘b’, ‘b’ is higher than the second ‘a’, the second ‘a’ is lower than ‘t’, and ‘t’ is higher than ‘e’. Note that “abated” does NOT flipflop, because ‘e’ is not lower than ‘d’ and “chatter” does NOT flipflop, because the first ‘t’ is not higher than the second ‘t’. The procedure’s declaration is as follows: void flipflops(const string & str, bool & flip, char & low, char & high); If the procedure determines that the input string flipflops, it must set the flip variable to true, the low variable to the lowest letter found in the string, and the high variable to the highest letter found in the string. If the procedure determines that the input string does not flipflop, it must set the flip variable to false and the low and high variables are left undefined. Notes:

• You may assume that “using namespace std;” and all necessary libraries are included at the beginning of the program.

• This procedure can be implemented in fewer than 25 lines of code.

Uniqname: ____________________________


Uniqname: ____________________________


Question 5 – Write some code (20 points) For this question, you must write the complete definition of a procedure, called findLongest, on the following page that analyzes the contents of a vector of integers to find the longest sequence of increasing values in the vector, writes this sequence to another vector, and then sums the contents of the sequence. The initial vector will only consist of positive integers except for the last value in the vector that will be set equal to the value -‐1. An example of the longest sequence of increasing values in the vector [1 4 5 2 5 7 9 10 5 6 -1] would be [2 5 7 9 10] and the sequence’s sum would be 33. Additionally, the longest sequence of increasing values in the vector [5 6 7 1 2 3 5 7 8 4 3 -1] would be [1 2 3 5 7 8] and the sequence’s sum would be 26. Finally, note that two adjacent integers with the same value constitute a break in a sequence. Thus, the longest sequence of increasing values in the vector [1 2 4 4 5 -1] would be [1 2 4] and the sequence’s sum would be 7. The procedure’s declaration is as follows: void findLongest(const vector <int> & inVec, vector <int> & outVec, int & sum); Once the procedure finds the longest sequence of increasing values in the vector inVec, it must first clear the contents of outVec and then write the contents of the sequence into outVec in the order that the sequence appeared in inVec. After writing the contents of the sequence into outVec, the procedure must write the sum of the integers contained in the sequence into the variable sum. Important Notes:

• You may assume that “using namespace std;” and all necessary libraries are included at the beginning of the program.

• Your solution must use only those vectors that are in the procedure’s parameter list and no more. In other words, you may not declare and/or use any vectors other than inVec and outVec in your solution.

• You may assume that there will be at least one sequence of increasing values in inVec whose length is greater than or equal 2. For example, [3 2 1 -1] and [7 7 7 -1] would both be considered invalid inputs for inVec.

• You may assume that there will be no ties for a longest sequence. For example, [5 6 2 3 -1] and [4 5 6 1 2 3 -1] would both be considered invalid inputs for inVec.

• This procedure can be implemented in fewer than 30 lines of code.

Uniqname: ____________________________


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