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160 EE Midterm 1 Spring 2008 Name: login id: Section: Team name: March 3, 2008 This is a open book, open notes, closed neighbor, closed teammate, closed laptop/cell phone/PDA/etc. exam. Partial credit is available, so where ever possible, Show Your Work, particularly when tracing the execution of programs. When writing code, it is NOT necessary to comment the code on this exam, however, you should use meaningful variable and function names to make your code readable. This exam consists of 10 numbered pages, including this cover sheet. You are advised to quickly look over the entire exam rst to plan your time. You will have as much time as you need for this exam (within reason), but should be able to complete it in about an hour. 1 1. (20 Points). Your co-worker was asked to write a program that reads in a start time (in hours and minutes), a count of appointments, and the duration of the appointments, in minutes. The program then prints a schedule for the day. For example, here is a sample run: enter the start time in hours minutes (EOF to quit): 7 30 enter number of appointments: 5 enter appointment duration: 20 Your appointments are at: 7:30 - 7:50 7:50 - 8:10 8:10 - 8:30 8:30 - 8:50 8:50 - 9:10 enter the start time in hours minutes (EOF to quit): Unfortunately, your co-worker forgot a lot of 160 stu . Make any required corrections to the code on the following page so that it will compile and execute correctly. Identify whether these errors would be detected at compile, link or run time. 2 #include <stdio.h> int next_hr(int length) main { int hours, mins; int flag; int appts; printf("enter the start time in hours minutes (EOF to quit): "); flag = scanf("%d %d", &hours, mins); while( hours != EOF) { printf("enter number of appointments: "); scanf("%d", &appts); printf("enter appointment duration: "); sanf("%d", &duration); printf("\nYour appointments are at:\n"); while(appts > 0); { printf("%2d:%2d - ", hours ); hours = hours + next hr(mins + duration); mins = (mins + duration) % 60; printf("%2d:%2d\n",hours,mins); printf("enter the start time in hours minutes (EOF to quit): "); scanf("%d } } int next_hr(int length); { return length/60; } ", &hours, &mins); 3 2. Show a manual trace and EXACT program output of the following programs (SHOW YOUR WORK): (a) (15 Points). The following program is compiled and run with input redirected from a le. The le has only the following three lines in it: 3 7 9 #include <stdio.h> main() { int x,y; int count = 0; scanf("%d", &x); while( scanf("%d", &y) != EOF) { printf("%d\t", y); while( y >= x ) { y = y - x; count = count + 1; } printf("%d\t%d\n", count, y); count = 0; } } 4 (b) (15 Points). int what( float x, float y); main() { float a, b; int x; a = 2.1; b = 7.6; x = 3; x = what( b, a ); b = a * x; printf("a = %4.2f, b = %f, x = %d\n", a, b, x ); a = what( b, x ); printf("a = %4.2f, b = %f, x = %d\n", a, b, x ); } int what( float a, float x) { float b; x = a - x; b = (int) a % (int) x; return b; } 5 3. Where s the Cheese? For the past 12 years, every Spring semester has been MicroMouse season when teams of EE students try to build autonomous robots that can solve a maze and compete for the honor of having the fastest mouse to nd the center. Your friend is on one of the teams this year and asked you for help testing a simple solving algorithm using your EE 160 skills. The competition maze is 16x16 cells, but we will use a bottom up approach and start with a much smaller maze of 3x3 cells shown below: North +---+---+---+ 2 | | | + + +---+ 1 | | | + + + + 0 | M | | +---+---+---+ 0 1 2 x South West y East The mouse starts in cell 0:0 facing North. It has sensors that can tell it if there are walls to its left, in front, and to its right which it reads in each cell to decide what to do next. For example, mouse the in cell (x:y) 0:0 above would see a left wall, no front wall, and a right wall, so its input would be 1 0 1. The mouse can turn 90 deg left or right or turn completely around (180 deg) in the the current cell, and can move forward one cell at a time. In each cell it reads the walls and decides what to do next. Our task is to write a simulator which will be given the walls the sees in each cell (read from a le), and determine what the mouse will do. We will use the ve step process to design this program. 6 (a) Understand the problem: The simple algorithm we will test is called a left wall hugger , meaning the mouse will always follow the wall on its left. So for this algorithm in the small maze shown above, the mouse will make the following moves, stopping when it returns to 0:0: Start in 0:0; facing North move forward to position 0:1 move forward to position 0:2 turn around; facing South move forward to position 0:1 turn left; facing East move forward to position 1:1 turn left; facing North move forward to position 1:2 turn right; facing East move forward to position 2:2 turn around; facing West move forward to position 1:2 turn left; facing South move forward to position 1:1 move forward to position 1:0 turn left; facing East move forward to position 2:0 turn left; facing North move forward to position 2:1 turn around; facing South move forward to position 2:0 turn right; facing West move forward to position 1:0 turn right; facing North move forward to position 1:1 turn left; facing West move forward to position 0:1 turn left; facing South move forward to position 0:0 (b) (15 Points). Do a hand example: To show you understand the left wall hugging algorithm, show the walls the mouse sees above in each cell (left, front, right) as it moves through the above maze in the path shown. To get you started, I give you the rst few steps below: Sees: l 1 1 1 f 0 0 1 r 1 0 1 so so so and Start in 0:0; facing North move forward to position 0:1 move forward to position 0:2 turn around; facing South move forward to position 0:1 7 (c) (15 Points). Write the algorithm: Write the algorithm for main() which will start the mouse in cell 0:0, read the walls from the input, and decide how to move, base on the walls it sees, and stops when it returns to 0:0. 8 (d) (20 Points). Translate the algorithm to C Before you write the code for main(), your friend has written several functions to help you implement your algorithm. The header le, move.h, is shown on the next page. You should use these functions in your code. (If you are interested, you can ask me for the code for these functions, move.c, but you don t need that to do this problem). Write the code for main() below: 9 /* file: move.h * by: team leader * date: 3 Mar 08 */ #define #define #define #define NORTH EAST WEST SOUTH 0 1 2 3 int turn_left(int direction); /* Given: the current direction the mouse is facing Returns: the new direction the mouse is facing after turning left Prints the turn and new direction. */ int turn_right(int direction); /* Given: the current direction the mouse is facing Returns: the new direction the mouse is facing after turning right Prints the turn and new direction. */ int turn_around(int direction); /* Given: the current direction the mouse is facing Returns: the new direction the mouse is facing after turning around Prints the turn and new direction. */ int forward_x(int x, int direction); /* Given: the x coordinate of the current cell the mouse is facing. Returns: the new x coordinate after the mouse */ int forward_y(int y, int direction); /* Given: the y coordinate of the current cell the mouse is facing. Returns: the new y coordinate after the mouse */ and the direction move one cell in that direction and the direction move one cell in that direction 10

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