#!C

#include <stdio.h>
#include <math.h>
#include <stdbool.h>

int calcE12Base(int n)
{
    int value = -1;

    if(n >= 1 && n <= 12)
    {
        value = round(10 * pow(10, (n-1)/12.0));
    }

    return value;
}

int realE12Base(int n)
{
    int value;

    switch(n)
    {
    case 1:
        value = 10;
        break;
    case 2:
        value = 12;
        break;
    case 3:
        value = 15;
        break;
    case 4:
        value = 18;
        break;
    case 5:
        value = 22;
        break;
    case 6:
        value = 27;
        break;
    case 7:
        value = 33;
        break;
    case 8:
        value = 39;
        break;
    case 9:
        value = 47;
        break;
    case 10:
        value = 56;
        break;
    case 11:
        value = 68;
        break;
    case 12:
        value = 82;
        break;
    default:
        value = -1;
    }

    return value;
}

double E12Value(int n, int p, bool calculate)
{
    double value = -1.0;

    if(calculate)
    {
        value = calcE12Base(n);
    }
    else
    {
        value = realE12Base(n);
    }

    if(value > 0 && p >= -3 && p <= 9)
    {
        value *= pow(10, p);
    }

    return value;
}

void printResistorValue(double value)
{
    double exponent = log10(value);
    int base1000exponent = (int) floor(exponent/3);
    char metricPrefix;
    value /= pow(10, base1000exponent * 3);

    switch (base1000exponent)
    {
        case -1 :
            metricPrefix = 'm';
            break;
        case 0 :
            metricPrefix = ' ';
            break;
        case 1 :
            metricPrefix = 'k';
            break;
        case 2 :
            metricPrefix = 'M';
            break;
        case 3 :
            metricPrefix = 'G';
            break;
    }
    if(value < 10)
    {
        printf("%3.1f%c", value, metricPrefix);
    }
    else
    {
        printf("%3.0f%c", value, metricPrefix);
    }
}

void printE12(bool calculate)
{
    for(int p = -3; p <= 9; p++)
    {
        for(int n = 1; n <= 12; n++)
        {
            printResistorValue(E12Value(n, p, calculate));
            printf(" ");
        }
        printf("\n");
    }
}

int main()
{
    printE12(true);

    printf("\n");

    printE12(false);

    return 0;
}

#!C
#include <stdio.h>
#include <stdbool.h>
#include <math.h>

/* Function to transfer color code from IEC 60062:2016 into an integer.
   returns 10 on error.

    Black   BK  0
    Brown   BN  1
    Blue    BU  6
    Gold    GD  -1
    Green   GN  5
    Gray    GY  8
    Orange  OG  3
    Pink    PK  -3
    Red     RD  2
    Silver  SR  -2
    Violet  VT  7
    Yellow  YE  4
*/

int colorCodeToInt(char c1, char c2)
{
    switch(c1)
    {
    case 'B':
        switch (c2)
        {
        case 'K':
            return 0;
        case 'N':
            return 1;
        case 'U':
            return 6;
        }
        break;
    case 'G':
        switch (c2)
        {
        case 'D':
            return -1;
        case 'N':
            return 5;
        case 'Y':
            return 8;
        }
        break;
    case 'O':
        if (c2 == 'G')
        {
            return 3;
        }
        break;
    case 'P':
        if (c2 == 'K')
        {
            return -3;
        }
        break;
    case 'R':
        if (c2 == 'D')
        {
            return 2;
        }
        break;
    case 'S':
        if (c2 == 'R')
        {
            return -2;
        }
        break;
    case 'V':
        if (c2 == 'T')
        {
            return 7;
        }
        break;
    case 'Y':
        if (c2 == 'E')
        {
            return 4;
        }
        break;
    }
    return 10;
}

int readBand(bool readSignificant)
{
    char c1, c2, dummy;
    int band;
    do
    {
        fflush(stdin); // clear keyboard buffer
        scanf("%c%c", &c1, &c2);
        band = colorCodeToInt(c1, c2);
        if (band == 10 || (readSignificant && band < 0))
        {
            printf("This is not a valid color code. Try again: ");
        }
    }
    while (band == 10 || (readSignificant && band < 0));
    return band;
}

// reuse printResistorValue from exercise 5.4
void printResistorValue(double value)
{
    double exponent = log10(value);
    int base1000exponent = (int) floor(exponent/3);
    char metricPrefix;
    value /= pow(10, base1000exponent * 3);

    switch (base1000exponent)
    {
        case -1 :
            metricPrefix = 'm';
            break;
        case 0 :
            metricPrefix = ' ';
            break;
        case 1 :
            metricPrefix = 'k';
            break;
        case 2 :
            metricPrefix = 'M';
            break;
        case 3 :
            metricPrefix = 'G';
            break;
    }
    if(value < 10)
    {
        printf("%3.1f%c", value, metricPrefix);
    }
    else
    {
        printf("%3.0f%c", value, metricPrefix);
    }
}

bool isE12(int value)
{
    switch(value)
    {
    case 10:
    case 12:
    case 15:
    case 18:
    case 22:
    case 27:
    case 33:
    case 39:
    case 47:
    case 56:
    case 68:
    case 82:
        return true;
    }
    return false;
}

int main(void)
{
    char answer, dummy;
    do
    {
        int band1, band2, band3;
        printf("Enter the first color code: ");
        band1 = readBand(true);
        printf("Enter the second color code: ");
        band2 = readBand(true);
        printf("Enter the third color code: ");
        band3 = readBand(false);
        printf("The value of this resistor is ");
        int significant = band1*10 + band2;
        printResistorValue(significant * pow(10, band3));
        printf("\n");
        if (isE12(significant))
        {
            printf("This value belongs to the E12 series\n");
        }
        else
        {
            printf("This value does not belong to the E12 series\n");
        }
        printf("Do you want to continue? ");
        do
        {
            fflush(stdin); // clear keyboard buffer
            scanf("%c", &answer);
            if (answer != 'Y' && answer != 'N')
            {
                printf("Not a valid answer. Try again (type Y or N): ");
            }
        }
        while (answer != 'Y' && answer != 'N');
    }
    while (answer == 'Y');
    return 0;
}