EE 160 Midterm 1. Spring Name: login id: Section: Team name: February 29, 2016

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1 EE 160 Midterm 1 Spring 2016 Name: login id: Section: Team name: February 29, 2016 This is a open book, open notes, closed neighbor, closed teammate, closed laptop/cell phone/ipad/etc. exam. You may also use your calculator for this 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 9 numbered pages, including this cover sheet. You are advised to quickly look over the entire exam first 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

2 1. Trace Me (25 Points). Show a manual trace of the following program, showing the values of all variables and the output generated by the program. (HINT: be careful of the types). The input file to the program is: (SHOW YOUR WORK) #include <stdio.h> float doit( int, float); main() { float a, b; int c, d; while( scanf("%f", &a)!= EOF) { scanf("%f", &b); d = b; c = doit(d, a); d = doit(c + 3, b) - doit(d, b); printf("its %d \n", d); float doit(int a, float b) { while( b >= a ) b = b - a; return b; 2

3 2. Fix Me (25 Points). In kindergarten we learned that if we drop a ball from different heights, it takes different amounts of time to hit the ground. Much later, in your Physics class you learned how to calculate how long an object takes to fall and its velocity in a constant gravity field. In the lab, you wrote programs to calculate the final velocity and height given the time. We would like to write a program that is given the initial height for dropping a ball, and shows the velocity and height at time intervals as the ball falls. The program on the next two pages is supposed to produce output like: Enter initial height (in m): 10 Time Velocity Height Ball hit ground at about time 1.4 sec (Note: the negative velocity and acceleration means in the down direction). But, my program doesn t work (where have I heard that before? :-)). Your job is to fix the errors in the code on the next 2 pages so that it compiles, links, and executes correctly. We know that the algorithm and formulas are correct, so, there are no logic errors, the problem is just in the code. For each error you fix, identify whether the error would have been detected at compile time, link time, or run time. 3

4 #include "stdio.h" float drop(float how_high, float how_fast) /* Given: initial height and velocity of ball Returns: prints table of height and velocity over time and returns time ball hit the ground. */ Main() { int flag; float height; /* get first height */ printf("enter initial height (in m): "); flag = scanf("%d", &height); /* while there are more trials to run */ while( height!= EOF) { /* print column headings */ printf("\n Time\t Velocity\t Height\n"); /* print one table */ splat = drop_ball(height, 0.0); /* print final result */ printf("\nball hit ground at about time %4.1f sec\n", splat) /* get next height */ printf("enter initial height (EOF to quit): " ; height = scan("%f", &flag); printf("\n"); 4

5 float drop(float ht, float velocity); /* Given: initial height and velocity of ball Returns: prints table of height and velocity over time and returns time ball hit the ground. */ { float time = 0.0; /* while the ball is still falling */ while( ht > 0); { /* print time step printf("%4.1f\t%10.2f\t%6.2f\n", time, velocity ); /* Update velocity over this interval */ velocity = velocity * 0.1; /* Update height over this interval */ ht = ht + velocity * 0.1; /* update time to next interval */ time = time + 0.1; /* ball hits the ground during this interval */ ht = 0; /* print velocity and height at end of interval */ printf("%4.1f\t%10.2f\t%6.2f\n, time, velocity, ht); return time; 5

6 3. MPG Most cars these days have on-board computers that can give the driver useful information like miles to next servce, or instantaneous miles per gallon. Being engineers, we like to figure out how do they do that?, so we d like to write a program that can compute the instanteneous and averge MPG using data from the on-board computer. We will use the five step process to design this program. (a) Understand the problem: For testing purposes, we will assume we can get data from the on-board computer in a file format consiting of a milage value (from the odometer) and a gallons of gas consumed value (measure by the fuel injectors) at regular intervals, say every 5 seconds. An example file might look like: With the above data, the program should produce the output: Instantaneous MPG = Instantaneous MPG = Instantaneous MPG = Instantaneous MPG = Instantaneous MPG = Instantaneous MPG = For 6 readings, average MPG = (b) (10 Points). Do a hand example: Use your calculator to show how to compute the first TWO lines of the above output. (results within +/ are sufficuent). 6

7 (c) (15 Points). Write the algorithm: Write the algorithm for this program. 7

8 (d) (20 Points). Translate the algorithm into C: Write the code for this program. 8

9 (e) (5 Points). Test the program: Explain to me in words what changes you would make to this program to compute the average speed from these measurements, given that the lines of input are at 5 second intervals. 9