A5: Asmt#5: Triangle area

Write a C program to do the following.

Input the unites of a triangle and the three points. Then print out the three points of the triangle, area of the triangle, and the direction of the three points. If the requirements are unclear in any way, use any provided input and output to resolve the discrepancy.

See Guidelines for C programs .

Note: The formula used was missing a factor of 0.5 so this assignment actually calculated twice the area of the triangle. This is, the parallelogram made up of two such triangles.

Domain knowledge is the background knowledge that is useful in solving a problem, designing a solution, implementing the solution, etc. The following domain knowledge may be useful for this requirement.

Area of a triangle

Note: In addition to specific domain knowledge, you should be familiar with all concepts covered to this point in the course.

The following coding examples and/or notes may be of use for this requirement.

Debugging via output
Read each line of input using one scanf function, then echo that line of input using one printf statement. Otherwise, if there is an issue, you will not know at which line the issue happened.
When reading a string using scanf after some other input, the previous input needs to have a "\n" at the end of the string.
Do not use an absolute value function. Instead, is an if-then-else statement.
When converting the area to an absolute value, do not change the original area variable. Instead, create a new variable and set that value to the absolute value. The general rule is to, after setting a variable to an initial value, never overwrite the variable with a new value unless necessary. Instead, create a new variable and initialize that variable to the desired value.

Make all necessary assumptions. Make no unnecessary assumptions.

In addition to specific coding examples, you should be familiar with all concepts covered to this point in the course.

The program inputs an integer variable (without prompt) that determines whether diagnostic output is shown according to the following values.

If 0, no extra output is shown, just the final results (no condition necessary)
If 1, output from processing and the final result, are shown (condition "greater than zero").
If 2, all output, including prompts and echo, is shown (condition "greater than one").

You are provided with the following starter program in file trianglearea.c.

Do not remove any comment that starts with three slashes.

Here is the C code.

/// File: trianglearea.c
/// Purpose: Triangle area
/// Author: (your name)
/// Help received:
// (add here)
/// pseudo-code:
// (add here)

#include <stdio.h>

int main() {
	///:BEGIN ToDo

	///:END ToDo
	return 0;
	}

You are to fill in the missing parts of the program according to the work requirements (see above).

In the comments at the top, you are to fill in the author (your name), help received (person and type of help), and pseudo-code parts which are not in the solution (usually provided, but you need to add them). Remove the parentheses too.

Begin solution

Here is a possible solution to the above problem. Note: Once a solution is provided, or the day before the next class, further submissions for this work receive no credit.

/// File: trianglearea.c
/// Purpose: Triangle area
/// Author: (your name)
/// Help received:
// (add here)
/// pseudo-code:
// (add here)

#include <stdio.h>

int main() {
	///:BEGIN ToDo
	// declarations
	int show1;
	char units1[256];
	double x0;
	double y0;
	double x1;
	double y1;
	double x2;
	double y2;
	double dx0;
	double dy0;
	double dx1;
	double dy1;
	double dx2;
	double dy2;
	double area1;
	double area2;
	// input
	// note: include \n to eat the newline so the string can be read
	scanf("%d\n",&show1);
	if (show1 > 1) {
		printf("Enter units of the triangle.\n");
		}
	scanf("%[^\n]s",&units1);
	if (show1 > 1) {
		printf("Units of the triangle are in %s\n",units1);
		printf("Enter points of the triangle.\n");
		}
	scanf("%lf %lf",&x0,&y0);
	if (show1 > 1) {
		printf("Point 1 is ( %lf , %lf )\n",x0,y0);
		}
	scanf("%lf %lf",&x1,&y1);
	if (show1 > 1) {
		printf("Point 2 is ( %lf , %lf )\n",x1,y1);
		}
	scanf("%lf %lf",&x2,&y2);
	if (show1 > 1) {
		printf("Point 3 is ( %lf , %lf )\n",x2,y2);
		}
	// process
	dx0 = 0.0;
	dy0 = 0.0;
	dx1 = x1 - x0;
	dy1 = y1 - y0;
	dx2 = x2 - x0;
	dy2 = y2 - y0;
	area1 = (dx1 * dy2) - (dx2 * dy1);
	if (area1 < 0.0) {
		area2 = - area1;
		}
	else {
		area2 = area1;
		}
	// output
	if (show1 > 0) {
		printf("\n");
		printf("Points and translated points:\n");
		printf("Point #0: ( %0.2lf , %0.2lf ) to ( %0.2lf , %0.2lf )\n",x0,y0,dx0,dy0);
		printf("Point #1: ( %0.2lf , %0.2lf ) to ( %0.2lf , %0.2lf )\n",x1,y1,dx1,dy1);
		printf("Point #2: ( %0.2lf , %0.2lf ) to ( %0.2lf , %0.2lf )\n",x2,y2,dx2,dy2);
		printf("\n");
		}
	printf("The triangle area is %0.2lf square %s\n",area2,units1);
	printf("The points go ");
	if (area1 > 0) {
		printf("counter-");
		}
	printf("clockwise.\n");
	///:END ToDo
	return 0;
	}

End solution

Here are some examples of input and output for the above program code.

Here is an example input from file input1.txt.

2
feet
1.0 1.0
3.0 2.0
2.0 3.0

For the above example input, here is the expected output.

Enter units of the triangle.
Units of the triangle are in feet
Enter points of the triangle.
Point 1 is ( 1.000000 , 1.000000 )
Point 2 is ( 3.000000 , 2.000000 )
Point 3 is ( 2.000000 , 3.000000 )

Points and translated points:
Point #0: ( 1.00 , 1.00 ) to ( 0.00 , 0.00 )
Point #1: ( 3.00 , 2.00 ) to ( 2.00 , 1.00 )
Point #2: ( 2.00 , 3.00 ) to ( 1.00 , 2.00 )

The triangle area is 3.00 square feet
The points go counter-clockwise.

Here is an example input from file input2.txt.

1
inches
1.0 1.0
2.0 3.0
3.0 2.0

For the above example input, here is the expected output.

Points and translated points:
Point #0: ( 1.00 , 1.00 ) to ( 0.00 , 0.00 )
Point #1: ( 2.00 , 3.00 ) to ( 1.00 , 2.00 )
Point #2: ( 3.00 , 2.00 ) to ( 2.00 , 1.00 )

The triangle area is 3.00 square inches
The points go clockwise.

Here is an example input from file input3.txt.

0
meters
2.1 3.2
1.8 4.6
1.2 1.8

For the above example input, here is the expected output.

The triangle area is 1.68 square meters
The points go counter-clockwise.

Pseudo-code is a "false" code. It is not really code, but a simplified English explanation that is somewhat similar to code. Pseudo-code is useful for understanding what a program does. For this work, the following can be used as the pseudo-code. Adjust if needed.

Get the units and points
Calculate the area and direction
Output the results

Note: Only some essential details are included. Some details, such as input, prompts, input echo, and obviously needed output are omitted.

The best way to copy-paste pseudo-code that includes indented code (e.g., with tabs) is as follows (in the code file) using a multi-line comment.

/* (pasted pseudo-code here) */

It is best to separate input, processing and output into different parts of a program.

Since C has limited string handling capabilities (they can get complex), some processing involving string processing is moved to the output section of the code.

CS 101 - A5 : Asmt#5: Triangle area Your grade: _ / 40 [LATE] Late or redo penalty: _ / -40 [SUBMIT] Not submitted properly: _ / -40 [RUN] Does not compile, run-time crash, etc.: _ / -40 [ETHICS] Ethical issues: _ / -40 [HEADER] Header comments not done as required: _ / -20 [STYLE] Inconsistant style or indentation: _ / -20 [CODE] Code guidelines ignored: _ / -40 [XCODE] Code used not yet covered: _ / -20 [REMOVED] Triple slash comments removed: _ / -20 [ADDED] Code added outside of marked areas: _ / -20 [OUTPUT] Functional requirements met: _ / 40 [CREDIT] Extra credit: _ / +8 Comments: