Debugging via output

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One way to help in debugging programs is to create output for every input and every calculation along the way.

This, however, makes for a lot of output and users may not want to see all of that output unless desired.

One way to handle this is to use a variable to turn the display of text on and off.

One can use an IDE (Integrated Development Environment) , such as Visual Studio, Eclipse, etc., that allows one to insect variables while the program is running.

However, this method does not always scale up to larger more complex programs.

The method presented here works for all types of programming systems.

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").

The measurement units are on the second line. Note that, in C, due to limited string handling capabilities, a "\n" is needed on the previous input statement to "eat" the newline in the input. Here is the C code.

#include <stdio.h>

int main() {
	// declarations
	int show1;
	char units1[256];
	double width1;
	double height1;
	double area1;
	// 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 square.\n");
		}
	scanf("%[^\n]s",&units1);
	if (show1 > 1) {
		printf("Units of the square are in %s\n",units1);
		printf("Enter width and height of the square.\n");
		}
	scanf("%lf %lf",&width1,&height1);
	if (show1 > 1) {
		printf("The width is %lf\n",width1);
		printf("The height is %lf\n",height1);
		}
	// process
	area1 = width1 * height1;
	// output
	if (show1 > 0) {
		printf("\n");
		printf("Square properties:\n");
		printf("\tWidth: %0.2lf %s\n",width1,units1);
		printf("\tHeight: %0.2lf %s\n",height1,units1);
		printf("\n");
		}
	printf("The square area is %0.2lf square %s.\n",area1,units1);
	return 0;
	}

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

Here is an example input.

2
feet
1.4 3.6

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

Enter units of the square.
Units of the square are in feet
Enter width and height of the square.
The width is 1.400000
The height is 3.600000

Square properties:
	Width: 1.40 feet
	Height: 3.60 feet

The square area is 5.04 square feet.

Here is an example input.

1
inches
6.4 3.2

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

Square properties:
	Width: 6.40 inches
	Height: 3.20 inches

The square area is 20.48 square inches.

Here is an example input.

0
miles
1.6 0.4

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

The square area is 0.64 square miles.

Below is the wrong way to do debugging with output. Do not write a separate program for each debugging case, as in the following program.

The following program consists of repeated code - code for each of the show cases. Do not do debugging output in this manner! Use the above example. Here is the C code.

#include <stdio.h>

int main() {
	// declarations
	int show1;
	char units1[256];
	double width1;
	double height1;
	double area1;
	// 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 square.\n");
		scanf("%[^\n]s",&units1);
		printf("Units of the square are in %s\n",units1);
		printf("Enter width and height of the square.\n");
		scanf("%lf %lf",&width1,&height1);
		printf("The width is %lf\n",width1);
		printf("The height is %lf\n",height1);
		area1 = width1 * height1;
		printf("\n");
		printf("Square properties:\n");
		printf("\tWidth: %0.2lf %s\n",width1,units1);
		printf("\tHeight: %0.2lf %s\n",height1,units1);
		printf("\n");
		printf("The square area is %0.2lf square %s.\n",area1,units1);
		}
	else if (show1 > 0) {
		scanf("%[^\n]s",&units1);
		scanf("%lf %lf",&width1,&height1);
		area1 = width1 * height1;
		printf("\n");
		printf("Square properties:\n");
		printf("\tWidth: %0.2lf %s\n",width1,units1);
		printf("\tHeight: %0.2lf %s\n",height1,units1);
		printf("\n");
		printf("The square area is %0.2lf square %s.\n",area1,units1);
		}
	else {
		scanf("%[^\n]s",&units1);
		scanf("%lf %lf",&width1,&height1);
		area1 = width1 * height1;
		printf("The square area is %0.2lf square %s.\n",area1,units1);
		}
	return 0;
	}

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

Here is an example input.

2
feet
1.4 3.6

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

Enter units of the square.
Units of the square are in feet
Enter width and height of the square.
The width is 1.400000
The height is 3.600000

Square properties:
	Width: 1.40 feet
	Height: 3.60 feet

The square area is 5.04 square feet.

Here is an example input.

1
inches
6.4 3.2

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

Square properties:
	Width: 6.40 inches
	Height: 3.20 inches

The square area is 20.48 square inches.

Here is an example input.

0
miles
1.6 0.4

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

The square area is 0.64 square miles.

Do not change show1 > 1 to show == 2 as one may want to add a show1 value of 3, 4, etc. in the future.

10. Acronyms and/or initialisms for this page

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