ENSF337-Lab 2 Solved

 Projectile Time and Distance Calculator 

Read This First 

In physics, assuming a flat Earth and no air resistance, a projectile launched with specific initial conditions will have a predictable range (maximum distance), and a predictable travel time. 

The range or maximum horizontal distance traveled by the projectile can be approximately calculated by: 

𝒗𝟐

𝒅 =   𝐬𝐢𝐧 (𝟐𝚯) 

𝒈

Where: g is gravitation acceleration (9.81 m/s2 ) 

θ: the angle at which the projectile is launched in degrees v: the velocity at which the projectile is launched d: the total horizontal distance travelled by the projectile 

To calulate the projectile travel time (t),  when it reaches the maximum horizontal distace the followig formaula can be used :  

𝟐𝒗𝒔𝒊𝒏𝚯

𝒕 =  

𝒈

In this exercise you will complete a given C source file called lab1exe_B.c that prompts the user to enter a projectile’s initial launch velocity () and displays the table of maximum horizontal distance and travel time for the trajectory angles of 0 to 90 degrees.  

What to Do:  
First, download file lab2exe_A.c from D2L. In this file the definition of function main and the function prototypes for four other functions are given. Your job is to complete the definition of the missing functions as follows:

Function create_table: which is called by the main function, receives the projectile initial velocity and displays a table of the projectile’s maximum travel distance (d) and time (t), for trajectory angles of 0 to 90 (degrees), with increments of 5 degrees. Here is the sample of the required table:

         Angle          t            d 

    (deg)        (sec)         (m) 

    0.000000     0.000000     0.000000   

    5.000000     1.778689     177.192018   

    10.000000    3.543840     349.000146 

You don’t have to worry about the format or the number of digits after the decimal point. The default format is acceptable.   

Function projectile_travel_time: receives two double arguments, the trajectory angle (), and the initial velocity () and returns the projectile travel time (t).

Function projectile_travel_distance: receives two double arguments, the trajectory angle (), and the initial velocity () and returns the projectile maximum horizontal distance (d).

Function degree_to_radian: receives an angle in degrees and converts to radian.  This function is needed, because the C library function sin needs its argument value to be in radian.

Notes:

•     To use the C library function sin, you need to include header file math.h.

•     When compiling from command line, if you are using Cygwin, Geany, or XCode, use –lm option to link the math library:

gcc -Wall –lm lab1exe_B.c 

•     For constant values of , and gravitation acceleration, g, the following lines are already included in the given file:

#define 3.141592654 

#define G 9.8   

Exercise B: Drawing AR Diagrams for a Simple C Program 
What to Do 
Download file lab2exe_B.c from D2L. Then, use pencil and paper to make memory diagrams for points one, two and three in the program.

Exercise C – Introduction to Pointers
Read This First 
This is an important exercise in ENSF 337. If you don't become comfortable with pointers, you will not be able to work with C. Spend as much time on this exercise as is necessary to understand exactly what is happening at every step in the given program.  

What to do 
Download the file lab2exe_C.c. Trace through the execution of the program to determine what the output will be.  
Now assume the following addresses for variables:  
  sam   9880   fred  9884   bar   9888   foo   9892 

Draw a set of AR diagrams for points two through five and use the given address numbers as values of the pointers (don't use arrow notation in this exercise).  

To understand how to draw these diagrams the solution for point one is given in the following figure: 

After you completed the exercise, compile lab2exe_C.c and check your predicted output against the actual program output.  

Exercise D: Pointers as function arguments 
What to do – Part I 
First copy the file lab2exe_D1.c from D2L. Carefully make diagrams for point one in this program using “Arrow Notation” as we discussed during lectures (you don’t need to use made-up addresses). Then compare your solution with the posted solution on D2L.

What to do – Part II
Now download the file lab2exe_D2.c from D2L and draw AR diagram for point one in this file, for pointers using arrow notation.

Exercise E: Using pointers to get a function to change variables 

What to do 
Make a copy of the file lab2exe_E.c from D2L.  If you try to compile and run this program it will give you some warning because the definition of function time_convert is missing.  

 Write the function definition for time_convert and add code to the main function to call time_convert before it prints answers.  

About the function interface comment 
The line minutes_ptr and seconds_ptr point to variables, appears in the REQUIRES section for the time_convert function. You might think that's useless information, but it's not. It is quite possible for a pointer argument to contain a garbage address, or a null pointer value, and in either of these cases the program would almost certainly crash. (You'll learn about null pointers later in the course.)  

Exercise F: More on scanf  
Read This First: 
scanf returns an integer number which indicates the number of input items that scanf has successful read from the keyboard. For example in the following code segment scanf is supposed to read three integer numbers and put them into the variables a, b, and c.   

int a, b, c, nscan;     

printf("Please Enter three integer values: "); nscan = scanf("%d%d%d", &a, &b, &c); 

if (nscan != 3) { 

   printf("Error: invalid input(s). I quit.\n\n");    exit(1); } 

To detect input error after calling scanf, a program must check the return value from scanf. If user enters invalid input, the return value of the scanf, nscanf, will have a value of zero, one, or two depending on how many of the inputs were properly entered. In this example, if nscanf is not equal to 3 the program will terminate using the exit() library function.

In general, scanf returns the number of items that it reads successfully, or returns EOF. EOF is a negative constant defined in <stdio.h>.The value EOF means that scanf reached the end of an input file or that some other error occurred.  

An important concept to understand about scanf (and many other C input functions) is that a C program sees input as a stream of characters, not as a sequence of lines of text. scanf will consume just enough characters to do its job, or to find out that it can't do its job. Remaining characters on the input stream are not consumed-instead they remain in the stream, waiting for the next input operation.  

 What To Do  - Part I; 
Copy the file lab2exe_F1.c from D2L. Read the program. Compile it, then run it several times, first with sensible input, then with various forms of bad input.  

For example observe what happens when you enter letters in response to the prompt for an integer? What if you type two integers on the same line? What if you type 67.89? What if you type one integer followed by letters? (You don't have to write down the answers.)  

An Explanation: 
The following picture shows what happened when you typed in 67.89 in response to the prompt for an integer.  The area of the memory that stores the stream of character inputs is called ‘buffer’.

The picture shows the stream of input characters after the first call to scanf was complete. Here is what the first call did:  

•       Read the '6', saw that it was a digit and could be used as part of an int.  

•       Read the '7', saw that it was a digit and could be used as part of an int.  

•       Read the '.', saw that it was not a digit and could be not be used as part of an int. The '.' was put back on the input stream so that it could be read by the next input operation.  

This is an important exercise. Don't hesitate to ask instructor or a TA for more information.  You will not be able to complete the next exercise if you do not fully understand this exercise.  

What to Do – Part II: 
Copy the file lab1exe_F2.c from D2L. Read the program. Compile it, then run it for 6 times, enter the inputs as listed in the following table, and complete the table for the values of n, i, and d. 

 Run # 
Your inputs 
What is the value of n 
What is the value of i 
What is the value d 
1 
12     0.56 
 
2 
5.12   9.56

 
3 
12     ab 
  
4 
ab     12 
  
5 
5ab    9.56 
 
6 
13     67