# Having hard time outputing the Band Color from a known value of a resistor [closed]

I'm writing a simple program to convert a Resistance Value to it's corresponding color bands. I'm trying to think of the most efficient way that will be universal for 4,5 and 6 Band Resistors. Inputting the color and calculating the resistance value is no problem. The other way around is really giving me a headache.

I tried using the log function from `<cmath>` library with a 4 band and succeeded. However, I cannot think of how to use it for 5 and 6 band resistors. Is there a way and if so is there a more efficient way that I haven't thought of yet. Below is my code using the log function built for a 4 band resistor.

Compiler: xcode

language: c++

``````#include <iostream>
#include <cmath>
using namespace std;
void band3_to_color(int);
void tolerance_to_color(float);
int main()
{
float r = 0.0f;
float t = 0.0f;
int exp = 0;
cout << "Enter Resistance: ";
cin >> r;
cout << "Enter Tolerance in Decimal Form: ";
cin >> t;
exp = log10( r / 10.f );
band3_to_color(r / pow(10,exp+1));
band3_to_color( (int( r / pow(10,exp ))) % 10);
band3_to_color(exp);
tolerance_to_color(t);
return 0;
}
void band3_to_color(int i){

if(i == 0) {cout << "| Black | ";}
else if(i == 1) {cout << "| Brown | ";}
else if(i == 2) {cout << "| Red | ";}
else if(i == 3) {cout << "| Orange | ";}
else if(i == 4) {cout << "| Yellow | ";}
else if(i == 5) {cout << "| Green | ";}
else if(i == 6) {cout << "| Blue | ";}
else if(i == 7) {cout << "| Violet | ";}
else if(i == 8) {cout << "| Gray | ";}
else {cout << "| White | ";}

}
void tolerance_to_color(float i){
if (i == .1){cout << "| Silver | ";}
else if(i == .05){cout << "| Gold | ";}
else if(i == .01){cout << "| Brown | ";}
else if(i == .02){cout << "| Red | ";}
else if(i == .005){cout << "| Green | ";}
else if(i == .0025){cout << "| Blue | ";}
else {cout << "| Purple | ";}
}
``````

Note the above was actually in a switch under a class. So I'm familiar with switch. I'm just trying to problem solve my formula or approach in making my log function work with 5 and 6 band.

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You really need to learn about `switch`... –  Florian Margaine Mar 31 '13 at 2:20
The above was actually in a switch under a class. So i'm familiar with switch. I'm just trying to problem solve my formula or approach in making my log function work with 5 and 6 band. –  Shane Yost Mar 31 '13 at 2:25

## closed as too localized by MainMa, thorsten müller, Martijn Pieters, Kilian Foth, MichaelTApr 1 '13 at 2:32

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I cannot think of how to use it for 5 and 6 band resistors.

Resistance values for 5- and 6-band resistors are specified in exactly the same way as 4-band resistors:

• The first three bands indicate a 3-digit resistance value.

• The fourth band indicates log10 of the multiplier.

• The 5th band, if present, specifies the tolerance.

• The 6th band, if present, specifies the temperature coefficient.

So, the user will have to specify more than just the resistance value if they want a 5- or 6-band response. You say that you're familiar with `switch`, so it shouldn't be a problem to simply switch on the additional input(s) to arrive at the extra band colors. In fact, you might want to use a series of `if` statements instead so that you can provide an appropriate output even if the user enters a non-standard value for the tolerance and temperature coefficient, like:

``````if (tolerance <= 0.05) { color = gray; }
else if (tolerance <= 0.1) { color = violet; }
else if (tolerance <= 0.25) { color = blue; }
...
``````
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