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resistor color code

Unpredictableimp (13)
ok. so i'm doing a school project where i have to make a program that:

1. Asks the user to enter
(a) A minimum resistance value RMIN.
(b) A maximum resistance value RMAX.
2. Computes, and prints to standard output,
(a) The mean (average) resistance value
R =1/2(RMIN + RMAX)
(b) A, B, and C, as described above.
(c) D: The tolerance percentage
TOL = (100*(RMAX - R))/R
3. Creates an image file called resistor.ppm, 200 pixels high, made up
of the following 10 or 11 vertical columns, each 20 pixels wide:
(a) Beige background. (Beige is R=.96, G=.96, B=.86.)
(b) A’s color code.
(c) Beige background.
(d) B’s color code.
(e) Beige background.
(f) C’s color code.
(g) Beige background, repeated twice. This second column creates a
wider gap between C and D.
(h) D’s color code, if it is gold or silver; if not, this last column is omitted.
(i) Beige background, repeated twice again

i have:

#include <iostream>
#include "csufmedia.h"
using namespace std;
int main ()
{
make_canvas(1, 200);

int A, B, C, D;
double tol, Rmin, Rmax, Ravg, R;

cout << "Enter a minimum value: ";
cin >> Rmin;
cout << "Enter a maximum value: ";
cin >> Rmax;
R = (Rmin + Rmax)/(2); //computing the average resistance
cout << "Resistance average = " << R << endl;

cout << "Enter a number 0-9 for A: ";
cin >> A;
cout << "Enter a number 0-9 for B: ";
cin >> B;
cout << "Enter a number 0-9 for C: ";
cin >> C;
cout << "Enter a number for D: ";
cin >> D;
tol = ((100*(Rmax - R))/(R)); //computes the tolerance
cout << "Tolerance = " << tol << endl;

cout << "Minimum resistance: " << Rmin << endl;
cout << "Maximum resistance: " << Rmax << endl;
cout << "A= " << A << endl;
cout << "B= " << B << endl;
cout << "C= " << C << endl;
cout << "D= " << D << endl;


switch(A)
{
case 0:
add_column(20, .96, .96, .86); //beige
add_column(20, 0, 0, 0); //black
add_column(20, .96, .96, .86); //beige
break;
case 1:
add_column(20, .96, .96, .86); //beige
add_column(20, .65, .16, .16); //brown
add_column(20, .96, .96, .86); //beige
break;
case 2:
add_column(20, .96, .96, .86); //beige
add_column(20, 1, 0, 0); //red
add_column(20, .96, .96, .86); //beige
break;
case 3:
add_column(20, .96, .96, .86); //beige
add_column(20, 1, .65, 0); //orange
add_column(20, .96, .96, .86); //beige
break;
case 4:
add_column(20, .96, .96, .86); //beige
add_column(20, 1, 1, 0); //yellow
add_column(20, .96, .96, .86); //beige
break;
case 5:
add_column(20, .96, .96, .86); //beige
add_column(20, 0, 1, 0); //green
add_column(20, .96, .96, .86); //beige
break;
case 6:
add_column(20, .96, .96, .86); //beige
add_column(20, 0, 0, 1); //blue
add_column(20, .96, .96, .86); //beige
break;
case 7:
add_column(20, .96, .96, .86); //beige
add_column(20, .93, .51, .93); //violet
add_column(20, .96, .96, .86); //beige
break;
case 8:
add_column(20, .96, .96, .86); //beige
add_column(20, .50, .50, .50); //gray
add_column(20, .96, .96, .86); //beige
break;
case 9:
add_column(20, .96, .96, .86); //beige
add_column(20, 1, 1, 1); //white
add_column(20, .96, .96, .86); //beige
break;
default:
cout << "That is not a number 0-9";
}


switch(B)
{
case 0:
add_column(20, 0, 0, 0); //black
add_column(20, .96, .96, .86); //beige
break;
case 1:
add_column(20, .65, .16, .16); //brown
add_column(20, .96, .96, .86); //beige
break;
case 2:
add_column(20, 1, 0, 0); //red
add_column(20, .96, .96, .86); //beige
break;
case 3:
add_column(20, 1, .65, 0); //orange
add_column(20, .96, .96, .86); //beige
break;
case 4:
add_column(20, 1, 1, 0); //yellow
add_column(20, .96, .96, .86); //beige
break;
case 5:
add_column(20, 0, 1, 0); //green
add_column(20, .96, .96, .86); //beige
break;
case 6:
add_column(20, 0, 0, 1); //blue
add_column(20, .96, .96, .86); //beige
break;
case 7:
add_column(20, .93, .51, .93); //violet
add_column(20, .96, .96, .86); //beige
break;
case 8:
add_column(20, .50, .50, .50); //gray
add_column(20, .96, .96, .86); //beige
break;
case 9:
add_column(20, 1, 1, 1); //white
add_column(20, .96, .96, .86); //beige
break;
default:
cout << "That is not a number 0-9";
}

switch(C)
{
case 0:
add_column(20, 0, 0, 0); //black
add_column(20, .96, .96, .86); //beige
add_column(20, .96, .96, .86); //beige
break;
case 1:
add_column(20, .65, .16, .16); //brown
add_column(20, .96, .96, .86); //beige
add_column(20, .96, .96, .86); //beige
break;
case 2:
add_column(20, 1, 0, 0); //red
add_column(20, .96, .96, .86); //beige
add_column(20, .96, .96, .86); //beige
break;
case 3:
add_column(20, 1, .65, 0); //
add_column(20, .96, .96, .86); //beige
add_column(20, .96, .96, .86); //beige
break;
case 4:
add_column(20, 1, 1, 0); //yellow
add_column(20, .96, .96, .86); //beige
add_column(20, .96, .96, .86); //beige
break;
case 5:
add_column(20, 0, 1, 0); //green
add_column(20, .96, .96, .86); //beige
add_column(20, .96, .96, .86); //beige
break;
case 6:
add_column(20, 0, 0, 1); //blue
add_column(20, .96, .96, .86); //beige
add_column(20, .96, .96, .86); //beige
break;
case 7:
add_column(20, .93, .51, .93); //violet
add_column(20, .96, .96, .86); //beige
add_column(20, .96, .96, .86); //beige
break;
case 8:
add_column(20, .50, .50, .50); //gray
add_column(20, .96, .96, .86); //beige
add_column(20, .96, .96, .86); //beige
break;
case 9:
add_column(20, 1, 1, 1); //white
add_column(20, .96, .96, .86); //beige
add_column(20, .96, .96, .86); //beige
break;
default:
cout << "That is not a number 0-9";
}


if(tol >= 0 || tol <= 5)
{
add_column(20, 1, .83, 0); //gold
add_column(20, .96, .96, .86); //beige
add_column(20, .96, .96, .86); //beige
}
else
if(tol >= 5.001 || tol <= 10)
{
add_column(20, .75, .75, .75); //silver
add_column(20, .96, .96, .86); //beige
add_column(20, .96, .96, .86); //beige
}
else
if(tol >= 10.001 || tol <= 20)
{
add_column(20, .96, .96, .86); //none so it defaults to background color, beige
add_column(20, .96, .96, .86); //beige
}

save_canvas("resistor.ppm");

return 0;
}

and when i check the ppm, the ones where D is supposed to be silver or none/beige turns out gold. could it be something with the if/else?
TheIdeasMan (6817)
Firstly, my omnipresent request to please edit your so it uses code tags the <> button on the right

With this code & the switches:

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switch(A)
{
case 0:
add_column(20, .96, .96, .86); //beige
add_column(20, 0, 0, 0); //black
add_column(20, .96, .96, .86); //beige
break;
case 1:
add_column(20, .96, .96, .86); //beige
add_column(20, .65, .16, .16); //brown
add_column(20, .96, .96, .86); //beige
break;


Each case has the colour beige for items 1 & 3, while the other is some other colour.

Can you write a function that takes the other colour as an argument, and carries out the 3 add_column function calls? You can do something similar for the other switches. This will improve the code considerably.

and when i check the ppm, the ones where D is supposed to be silver or none/beige turns out gold. could it be something with the if/else?


if(tol >= 0 || tol <= 5)

Use the && oprator instead of the OR operator.

Am interested to see how you go, can you post your code again after you make the changes? Don't for get the code tags

Edit:

There could be a problem with your if statements, because of the comparison of the double types.

Floating Point (floats & doubles) are represented as binary fractions and not all real numbers can be represented exactly. The problem with this code:

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if(tol >= 0 || tol <= 5) {
//code
}
else if (tol >= 5.001 || tol <= 10) {
//code
}


The tol <= 5.0 will fail if tol is 5.0, because tol is probably something like 5.0 + 1e-15, so the equality test fails. It is not caught with the next else if clause, because of the tol >= 5.001

The answer to al this is to make use of numeric_limits<double>epsilon. This is the distance to the next representable number greater than 1.0. It needs to be scaled up for the number being compared. To check for equality, you need to work out the absolute value of the difference between your number and the comparison number. Then compare this to the scaled up epsilon.

Last edited on
Unpredictableimp (13)
awesome thanks! i just changed 
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if(tol >= 0 || tol <= 5)
		{
			add_column(20, 1, .83, 0); //gold
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
		}
	else
		if(tol >= 5.001 || tol <= 10)
		{
			add_column(20, .75, .75, .75); //silver
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
		}
	else 
		if(tol >= 10.001 || tol <= 20)
		{
			add_column(20, .96, .96, .86); //none so it defaults to background color, beige
			add_column(20, .96, .96, .86); //beige
		}


to

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if(tol >= 0 && tol <= 5)
		{
			add_column(20, 1, .83, 0); //gold
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
		}
	else
		if(tol >= 5.001 && tol <= 10)
		{
			add_column(20, .75, .75, .75); //silver
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
		}
	else 
		if(tol >= 10.001 && tol <= 20)
		{
			add_column(20, .96, .96, .86); //none so it defaults to background color, beige
			add_column(20, .96, .96, .86); //beige
		}


and it works perfect. um, we haven't learned numeric_limits<double>epsilon in class yet so that's why i didn't use it and the numbers i used in the if/else where given to me in the instructions

so now my code looks like 

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#include <iostream>
#include "csufmedia.h"
using namespace std;
int main ()
{
	make_canvas(1, 200);
	
	int A, B, C, D;
	double tol, Rmin, Rmax, Ravg, R;

	cout << "Enter a minimum value: ";
	cin >> Rmin;
	cout << "Enter a maximum value: ";
	cin >> Rmax;
	R = (Rmin + Rmax)/(2); //computing the average resistance
	cout << "Resistance average = " << R << endl;
	
	cout << "Enter a number 0-9 for A: ";
	cin >> A;
	cout << "Enter a number 0-9 for B: ";
	cin >> B;
	cout << "Enter a number 0-9 for C: ";
	cin >> C;
	cout << "Enter a number for D: ";
	cin >> D;
	tol = ((100*(Rmax - R))/(R)); //computes the tolerance
	cout << "Tolerance = " << tol << endl;
	
	cout << "Minimum resistance: " << Rmin << endl;
	cout << "Maximum resistance: " << Rmax << endl;
	cout << "A= " << A << endl;
	cout << "B= " << B << endl;
	cout << "C= " << C << endl;
	cout << "D= " << D << endl;
	

	switch(A)
	{
		case 0:
			add_column(20, .96, .96, .86); //beige
			add_column(20, 0, 0, 0); //black
			add_column(20, .96, .96, .86); //beige
			break;	
		case 1:
			add_column(20, .96, .96, .86); //beige
			add_column(20, .65, .16, .16); //brown
			add_column(20, .96, .96, .86); //beige
			break;	
		case 2:
			add_column(20, .96, .96, .86); //beige
			add_column(20, 1, 0, 0); //red
			add_column(20, .96, .96, .86); //beige
			break;	
		case 3:
			add_column(20, .96, .96, .86); //beige
			add_column(20, 1, .65, 0); //orange
			add_column(20, .96, .96, .86); //beige
			break;	
		case 4:
			add_column(20, .96, .96, .86); //beige
			add_column(20, 1, 1, 0); //yellow
			add_column(20, .96, .96, .86); //beige
			break;	
		case 5:
			add_column(20, .96, .96, .86); //beige
			add_column(20, 0, 1, 0); //green
			add_column(20, .96, .96, .86); //beige
			break;	
		case 6:
			add_column(20, .96, .96, .86); //beige
			add_column(20, 0, 0, 1); //blue
			add_column(20, .96, .96, .86); //beige
			break;	
		case 7:
			add_column(20, .96, .96, .86); //beige
			add_column(20, .93, .51, .93); //violet
			add_column(20, .96, .96, .86); //beige
			break;	
		case 8:
			add_column(20, .96, .96, .86); //beige
			add_column(20, .50, .50, .50); //gray
			add_column(20, .96, .96, .86); //beige
			break;	
		case 9:
			add_column(20, .96, .96, .86); //beige
			add_column(20, 1, 1, 1); //white
			add_column(20, .96, .96, .86); //beige
			break;	
		default:
			cout << "That is not a number 0-9";
	}


	switch(B)
	{
		case 0:
			add_column(20, 0, 0, 0); //black
			add_column(20, .96, .96, .86); //beige
			break;	
		case 1:
			add_column(20, .65, .16, .16); //brown
			add_column(20, .96, .96, .86); //beige
			break;	
		case 2:
			add_column(20, 1, 0, 0); //red
			add_column(20, .96, .96, .86); //beige
			break;	
		case 3:
			add_column(20, 1, .65, 0); //orange
			add_column(20, .96, .96, .86); //beige
			break;	
		case 4:
			add_column(20, 1, 1, 0); //yellow
			add_column(20, .96, .96, .86); //beige
			break;	
		case 5:
			add_column(20, 0, 1, 0); //green
			add_column(20, .96, .96, .86); //beige
			break;	
		case 6:
			add_column(20, 0, 0, 1); //blue
			add_column(20, .96, .96, .86); //beige
			break;	
		case 7:
			add_column(20, .93, .51, .93); //violet
			add_column(20, .96, .96, .86); //beige
			break;	
		case 8:
			add_column(20, .50, .50, .50); //gray
			add_column(20, .96, .96, .86); //beige
			break;	
		case 9:
			add_column(20, 1, 1, 1); //white
			add_column(20, .96, .96, .86); //beige
			break;	
		default:
			cout << "That is not a number 0-9";
	}

	switch(C)
	{
		case 0:
			add_column(20, 0, 0, 0); //black
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
			break;	
		case 1:
			add_column(20, .65, .16, .16); //brown
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
			break;	
		case 2:
			add_column(20, 1, 0, 0); //red
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
			break;	
		case 3:
			add_column(20, 1, .65, 0); //
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
			break;	
		case 4:
			add_column(20, 1, 1, 0); //yellow
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
			break;	
		case 5:
			add_column(20, 0, 1, 0); //green
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
			break;	
		case 6:
			add_column(20, 0, 0, 1); //blue
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
			break;	
		case 7:
			add_column(20, .93, .51, .93); //violet
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
			break;	
		case 8:
			add_column(20, .50, .50, .50); //gray
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
			break;	
		case 9:
			add_column(20, 1, 1, 1); //white
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
			break;	
		default:
			cout << "That is not a number 0-9";
	}


	if(tol >= 0 && tol <= 5)
		{
			add_column(20, 1, .83, 0); //gold
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
		}
	else
		if(tol >= 5.001 && tol <= 10)
		{
			add_column(20, .75, .75, .75); //silver
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
		}
	else 
		if(tol >= 10.001 && tol <= 20)
		{
			add_column(20, .96, .96, .86); //none so it defaults to background color, beige
			add_column(20, .96, .96, .86); //beige
		}

	save_canvas("resistor.ppm");

	return 0;
}
TheIdeasMan (6817)
and it works perfect.


Really? How many values did you test it with? Testing doesn't mean trying a few values. To give you an idea, I write code to test my functions, so I can test lots of values, and especially values which have potential to fail, or are near boundaries - in this case values of 5 & 10.

and the numbers i used in the if/else where given to me in the instructions


That may be so, but you have holes in the logic, because any number between 5.0 and 5.001 & 10.0 and 10.001 "falls through" . That is something that should be fixed.

BTW else if looks like this:
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if(tol >= 0 && tol <= 5) {
	add_column(20, 1, .83, 0); //gold
	add_column(20, .96, .96, .86); //beige
	add_column(20, .96, .96, .86); //beige
}
else if(tol >= 5.001 && tol <= 10)  {
	add_column(20, .75, .75, .75); //silver
	add_column(20, .96, .96, .86); //beige
	add_column(20, .96, .96, .86); //beige
}
else if(tol >= 10.001 && tol <= 20) {
	add_column(20, .96, .96, .86); //none so it defaults to background color, beige
	add_column(20, .96, .96, .86); //beige
}
else {
//fix errors here
}


With what I was saying about reducing down the switches:

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add_column(20, .96, .96, .86); //beige
switch(A)
	{
		case 0:
			add_column(20, 0, 0, 0); //black
			break;	
		case 1:
			add_column(20, .65, .16, .16); //brown
			break;	
//similar for other cases
      } //end of switch
add_column(20, .96, .96, .86); //beige


You could do something similar for the other switches.

I notice you don't do anything with variable D.
ne555 (10692)
@TheIdeasMan:
> BTW else if looks like this:
Don't impose your formatting rules.
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if( condition )
   statement
[ else
   statement ]


@OP: you don't seem to understand what `else' means. 
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if( n<42 )
   foo();
else //here n>=42, you don't need to recheck that
   bar();

TheIdeasMan (6817)
@ne555

Don't impose your formatting rules.


Not really my formatting rules.

The OP had:
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if( condition )
   statements
else
if( condition )
   statements
else
if( condition )
   statements


I was proposing:

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if( condition )
   statements
else if( condition )
   statements 
else if( condition )
   statements
else
  statements


This was because the OP probably wasn't aware of the else if clause, and the else to catch any other value.
killax (2)
Weren't you suppose to figure out how how to compute the values of A, B, and C instead of inputting them?
Unpredictableimp (13)
well the instructions for the project was a little unclear. i know that if/else should look like 

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if( condition )
   statements
else if( condition )
   statements 
else if( condition )
   statements
else
  statements


but i was only given the table

Tolerance Color R G B
0–5% gold 1 .83 0
5.001–10% silver .75 .75 .75
10.001-20% (none) – – –

i thought of doing 
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if(tol >= 0 && tol <= 5)
		{
			add_column(20, 1, .83, 0); //gold
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
		}
	else
		if(tol >= 5.001 && tol <= 10)
		{
			add_column(20, .75, .75, .75); //silver
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
		}
	else 
		{
			add_column(20, .96, .96, .86); //none so it defaults to background color, beige
			add_column(20, .96, .96, .86); //beige
		}

but in the table for none the tolerance is 10.001-20%, so....

@TheIdeasMan:
the professor wants us to turn in the
Input and output, and the corresponding PPM file, for the three examples
given earlier.
and when i tried those, it worked.
i'm fairly new at C++ so i didn't realize that i could reduce the switch statements to 
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add_column(20, .96, .96, .86); //beige
switch(A)
	{
		case 0:
			add_column(20, 0, 0, 0); //black
			break;	
		case 1:
			add_column(20, .65, .16, .16); //brown
			break;	
      } 
add_column(20, .96, .96, .86); //beige


@killax:
.....i hate you....but love you for pointing that out. now i know where that other equation comes in. crud. that changes the first part then.....

so now new question:
i'm given the equation A.B x 10^C +- D%, i assume that i'll be using the Rmin and Rmax values that the user inputs to figure out A, B, and C. but since the professor hasn't gone over base and exponent. can anyone help or refer me to something that can help me?
Last edited on
TheIdeasMan (6817)
To compute exponents, you can use the pow function, which is found in the math library - #include<cmath>

HTH
killax (2)
To find C, you must put #include <math.h>
the formula for C is C=floor(log10(R));
i don't know about A and B though.
Unpredictableimp (13)
i got it to where it computes C right but i don't know how to get A and B. so far i've got:
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	int A, B, C, D, AB;
	double Rmin, Rmax, R;

	cout << "Enter a minimum value: ";
	cin >> Rmin;
	cout << "Enter a maximum value: ";
	cin >> Rmax;
	R = (Rmin + Rmax)/(2); //computing the average resistance
	cout << "Resistance average = " << R << endl;
	D = ((100*(Rmax - R))/(R)); //computes the tolerance
	C=floor(log10(R));
	AB=D/pow(10.0, (C-1));
	A=(AB/10);
	B=(AB%10);

but A and B comes out as 0
Last edited on
TheIdeasMan (6817)
AB=D/(10^(C-1));

I am guessing this is psuedo code. To calculate an exponent use the pow function.

AB=D/(pow(10,(C-1)));

The ^ operator is the bitwise XOR operator, hence the answers of zero.

I find it always pays to check out all the functions / operators you are using, so you can understand how they work.

http://www.cplusplus.com/doc/tutorial/operators/


HTH
Unpredictableimp (13)
i got it!
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int A, B, C, D, AB;
	double Rmin, Rmax, R;

	cout << "Enter a minimum value: ";
	cin >> Rmin;
	cout << "Enter a maximum value: ";
	cin >> Rmax;
	R = (Rmin + Rmax)/(2); //computing the average resistance
	cout << "Resistance average = " << R << endl;
	D = ((100*(Rmax - R))/(R)); //computes the tolerance
	C=floor(log10(R));
	AB=R/pow(10.0,C-1);
	A=(AB/10);
	B=(AB%10);

it works now :p
TheIdeasMan (6817)
#include <math.h>

This is the C version. The following is the C++ version:

#include<cmath>


Unpredictableimp (13)
ok so it works now where A, B, and C is computed (thanks killax for pointing that out) so now it looks like this

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#include <iostream>
#include "csufmedia.h"
#include <cmath>
using namespace std;
int main ()
{
	make_canvas(1, 200);
	
	int A, B, C, D, AB;
	double Rmin, Rmax, R;

	cout << "Enter a minimum value: ";
	cin >> Rmin;
	cout << "Enter a maximum value: ";
	cin >> Rmax;
	R = (Rmin + Rmax)/(2); //computing the average resistance
	cout << "Resistance average = " << R << endl;
	D = ((100*(Rmax - R))/(R)); //computes the tolerance
	C=floor(log10(R));
	AB=R/pow(10.0,C-1);
	A=(AB/10);
	B=(AB%10);
	
	cout << "Minimum resistance: " << Rmin << endl;
	cout << "Maximum resistance: " << Rmax << endl;
	cout << "A= " << A << endl;
	cout << "B= " << B << endl;
	cout << "C= " << C << endl;
	cout << "D= " << D << endl;
	
	add_column(20, .96, .96, .86); //beige
	switch(A)
	{
		case 0:
			add_column(20, 0, 0, 0); //black
			break;	
		case 1:
			add_column(20, .65, .16, .16); //brown
			break;	
		case 2:
			add_column(20, 1, 0, 0); //red
			break;	
		case 3:
			add_column(20, 1, .65, 0); //orange
			break;	
		case 4:
			add_column(20, 1, 1, 0); //yellow
			break;	
		case 5:
			add_column(20, 0, 1, 0); //green
			break;	
		case 6:
			add_column(20, 0, 0, 1); //blue
			break;	
		case 7:
			add_column(20, .93, .51, .93); //violet
			break;	
		case 8:
			add_column(20, .50, .50, .50); //gray
			break;	
		case 9:
			add_column(20, 1, 1, 1); //white
			break;	
		default:
			cout << "That is not a number 0-9";
	}
	add_column(20, .96, .96, .86); //beige

	switch(B)
	{
		case 0:
			add_column(20, 0, 0, 0); //black
			break;	
		case 1:
			add_column(20, .65, .16, .16); //brown
			break;	
		case 2:
			add_column(20, 1, 0, 0); //red
			break;	
		case 3:
			add_column(20, 1, .65, 0); //orange
			break;	
		case 4:
			add_column(20, 1, 1, 0); //yellow
			break;	
		case 5:
			add_column(20, 0, 1, 0); //green
			break;	
		case 6:
			add_column(20, 0, 0, 1); //blue
			break;	
		case 7:
			add_column(20, .93, .51, .93); //violet
			break;	
		case 8:
			add_column(20, .50, .50, .50); //gray
			break;	
		case 9:
			add_column(20, 1, 1, 1); //white
			break;	
		default:
			cout << "That is not a number 0-9";
	}
	add_column(20, .96, .96, .86); //beige

	switch(C)
	{
		case 0:
			add_column(20, 0, 0, 0); //black
			break;	
		case 1:
			add_column(20, .65, .16, .16); //brown
			break;	
		case 2:
			add_column(20, 1, 0, 0); //red
			break;	
		case 3:
			add_column(20, 1, .65, 0); //orange
			break;	
		case 4:
			add_column(20, 1, 1, 0); //yellow
			break;	
		case 5:
			add_column(20, 0, 1, 0); //green
			break;	
		case 6:
			add_column(20, 0, 0, 1); //blue
			break;	
		case 7:
			add_column(20, .93, .51, .93); //violet
			break;	
		case 8:
			add_column(20, .50, .50, .50); //gray
			break;	
		case 9:
			add_column(20, 1, 1, 1); //white
			break;	
		default:
			cout << "That is not a number 0-9";
	}
	add_column(20, .96, .96, .86); //beige
	add_column(20, .96, .96, .86); //beige

	if(D >= 0 && D <= 5)
		{
			add_column(20, 1, .83, 0); //gold
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
		}
	else
		if(D >= 5.001 && D <= 10)
		{
			add_column(20, .75, .75, .75); //silver
			add_column(20, .96, .96, .86); //beige
			add_column(20, .96, .96, .86); //beige
		}
	else 
		if(D >= 10.001 && D <= 20)
		{
			add_column(20, .96, .96, .86); //none so it defaults to background color, beige
			add_column(20, .96, .96, .86); //beige
		}

	save_canvas("resistor.ppm");

	return 0;
}


thanks for the help. is there anything else that i can improve?
TheIdeasMan (6817)
Tolerance Color R G B
0–5% gold 1 .83 0
5.001–10% silver .75 .75 .75
10.001-20% (none) – – –


Just going back to my earlier comments about the holes in the logic for the output values.

Your professor may have given those numbers, but you could get brownie points for doing this properly & pointing out the problem. The 3 decimal places in those numbers is a clue to the expected precision of your output.

At the moment if variable D is anywhere between 5.0 and 5.001 or 10.0 and 10.001, no action is carried out. Also there is no else clause to catch error values for the value of variable D.

I am not sure that you understand how floating point values work.

They are stored as binary fractions, so that cannot represent all real values. For this reason, comparisons often fail:

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float a = 0.1; // a == 0.09999997
float b = 10 * a;  //b == 0.9999997
if (b == 1.0) //false


Changing the type to double does not fix the problem.

To do the equality comparison properly, you need to work out the absolute value of your number less the comparison number. This needs to be compared to a scaled up epsilon value.

numeric_limits<double>epsilon is the difference between 1.0 and the next representable value and is about 1.0e-16. This value needs to be multiplied by the number you are dealing with.

The other alternative is to use a user precision ( in your case 0.001). You can follow the algorithm above using this precision rather than the epsilon value, but there can still be problems and you might find yourself having to use the epsilon value as well.

One potential problem is when you get values that are a smidgin less than zero (-1.0e-14 say) as opposed to a smidgin above zero. Note that a calculated double is almost never zero exactly, and it is exceedingly rare that whole numbers calculate exactly. So you need to check that you value is greater than 0.0 - epsilon.

I hope this shown some of the myriad of problems associated with floating point numbers (doubles & floats).
Last edited on
Unpredictableimp (13)
yes i realize that there will be holes in my code. i'm just learning C++ and we haven't gone over numeric_limits<double>epsilon in class. what i've been trying to say is that i can't use things in the code that i haven't even learned yet. my code is based off of what we have gone over.
TheIdeasMan (6817)
OK, at least change the if conditions, so they form a contiguous range, and the else clause:

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if(D >= 0.0 && D <= 5.0) {

}
else if(D >= 5.0 && D <= 10.0) {

}
else if(D >= 10.0 && D <= 20.0) {

}
else { //catch any other value
//error processing here
}


You could still do what I was saying in my last post, but use you user precision of 0.001, that will catch most of the floating point errors. It's not that hard to do - and could get you brownie points from your professor.
Last edited on
Troyque (1)
here i am a new member and i have no any idea.... :(
TheIdeasMan (6817)
@Troyque (1)

Don't make pointless posts like that, you could easily be reported to admin.

If you have a question, ask it. Or if you have something meaningful to contribute, then do it.

Topic archived. No new replies allowed.