CSci 1113 Midterm 2. Name: Student ID:

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1 CSci 1113 Midterm 2 Name: Student ID: Instructions: Please pick and answer any 6 of the 8 problems for a total of 90 points. If you answer more than 6 problems, only the first 6 will be graded. The time limit is 50 minutes. Please write your answers in the space provided. The exam is open book and notes. You may use electronic devices to ONLY look at either an e-book version or electronic notes. You may not use the internet, compiler or any other outside resources. (If you are typing on your keyboard/input device for anything other than ctrl-f to find words in the e-book or notes, this is probably not acceptable.) Problem (1) [15 points] Suppose there exists a file in the current directory called examsolutions.txt. Write C++ code to copy everything from this file into a new file called myanswers.txt. You must ensure that the original file and the new one are identical. Your program does not need to detect if there is an error when using the files. You may assume proper #includes have been done for you. Provide a main() function that gives the functionality described above. ifstream input; input.open("examsolutions.txt"); ofstream output; output.open("myanswers.txt"); string line; getline(input, line); while(!input.eof()) output << line << endl; getline(input, line); 1

2 Problem (2) [15 points] Write a C++ code segment (as if it was in main()) that reads in from the keyboard and copies that directly to a file called texttofile.txt. This should continue copying what was typed on the keyboard until they type (after pressing enter on the last line)!exit. This!exit should not appear in the file. If they enter more than just!exit, such as!exitz, you would add this to the file. When writing to the file, do not include any enter key from the user as newlines (it should be one long run-on line). Your program must check for any errors when trying to write the file. If an error occurs, halt the program. An example terminal input and text file are given below: ofstream output; output.open("texttofile.txt"); if(output.fail()) cout << "ERROR"; exit(0); string line; getline(cin, line); while(line!= "!exit") output << line; getline(cin, line); Keyboard input hello th ere, how are you?!exit File result hello there, how are you? 2

3 Problem (3) [15 points] Write (in C++) the function afterspace() that takes a C++ string (i.e. from the string class) as an input. Return the character after the first space in the input string. For example the function call below will display: w string words = "hello world yahooo"; cout << afterspace(words); char afterspace(string s) return s.at(s.find( )+1); 3

4 Problem (4) [15 points] Write a C++ function that overloads the following distance() function to work for three doubles as an input. The function should return the correct Euclidean distance from the origin to the point specified by the 3 doubles in 3-dimensional space. The formula for an n dimensional Euclidean distance for the point p = (d 1, d 2,...d n ) ni=1 is: d 2 i. double distance(double x, double y) return sqrt(x*x + y*y); double distance(double x, double y, double z) return sqrt(x*x + y*y + z*z); 4

5 Problem (5) [15 points] Write a recursive function that finds the factorial of an integer, n! = n (n 1) (n 2) The recursive function, called factorial(), should take as input a single integer and return the value of the factorial. Give C++ code for the recursive function, an example main() function call is provided below: cout << factorial(5); // should display 120 int factorial(int n) if(n==0) return 1; return n*factorial(n-1); 5

6 Problem (6) [15 points] Write (in C++) a function that takes as input a 2-dimensional array of doubles, called grades, along with the number of rows, called rows. The grades variable has 10 columns (i.e. grades[ ][10]). This function should do the following: on even rows (0, 2, 4, 6,...), you should increase each grade (in every column) by 10%, and on odd rows you should subtract 10 from the grade. Ensure that you change grades directly. void fixgrades(double grades[][10], int nrows) for(int i=0; i < nrows; i++) for(int j=0; j < 10; j++) if(i%2 == 0) grades[i][j] *= 1.1; else grades[i][j] -= 10; 6

7 Problem (7) [15 points] Write (in C++) the function averages() that takes an array, the array size and two integers as input. Assuming the array is sorted, store the value of the mean and median in the last two integers (in that order) and make this change reflect where the function was called from. If there is an even number of elements in the array, the median can be either middle number. Below is an example usage in main() with commented proper output: int numbers[] = 1,2, 3,6; // THIS ARRAY IS SORTED int mean, median; averages(numbers, 4, mean median); cout << "Mean is " << mean << endl; // displays: 3 cout << "Median is " << median << endl; // displays: 2 or 3 void averages(int nums[], int len, int& mean, int& median) int sum=0; for(int i=0; i < len; i++) sum += nums[i]; mean = sum/len; median = nums[len/2]; 7

8 Problem (8) [15 points] Find 3 possible places for errors in the following code. Assume there is no problem with the use of the rand() function. Also assume no variables are global. Explain specifically what causes each error and whether it is a syntax or logic error: int random Element(char array, int size) if(size > 0) int randindex = rand()%size; else return 0; return array[randindex]; 1. int random Element(char array, int size) Syntax, the function name is split with a space 2. int random Element(char array, int size) Syntax, the return line uses it as an array, but it is not passed in as one. 3. return array[randindex]; Syntax, randindex is out of scope 4. return array[randindex]; Logic, your declaration says it will return an int, not a char... 8