优化转换算法

Question

I have recently been working on a exercise in a book I have been reading. The task was to create a program that prints all the numbers between 1-256 in their binary, octal and hexadecimal equivalents. We were only supposed to use methods we had learned so far in the book, which meant only using for, while and do..while loops, if and else if statements, converting integers to ASCII equivalents and some more basic stuff (eg cmath and iomanip).

So after some work, here is my result. However, it is messy and un-elegant and obfuscated. Does anyone have any suggestions to increase code efficiency (or elegance... :P) and performance?

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

int main()
{
int decimalValue, binaryValue, octalValue, hexadecimalValue, numberOfDigits;
cout << "Decimal\t\tBinary\t\tOctal\t\tHexadecimal\n\n";
for (int i = 1; i <= 256; i++)
{
    binaryValue = 0;
    octalValue = 0;
    hexadecimalValue = 0;
    if (i != 0) 
    {
    int x, j, e, c, r = i, tempBinary, powOfTwo, tempOctal, tempDecimal;
    for (j = 0; j <=8; j++) //Starts to convert to binary equivalent
    {
        x = pow(2.0, j);
        if (x == i)
        {
              powOfTwo = 1;
              binaryValue = pow(10.0, j);
              break;
        }
        else if (x > i)
        {
              powOfTwo = 0;
              x /= 2;
              break;
        }
    }
    if (powOfTwo == 0)
    {
    for (int k = j-1; k >= 0; k--)
    {
        if ((r-x)>=0)
        {
           r -= x;
           tempBinary = pow(10.0, k);
           x /= 2;
        }
        else if ((r-x)<0)
        {
           tempBinary = 0;
           x /= 2;
        }
        binaryValue += tempBinary;
    }
    } //Finished converting
    int counter = ceil(log10(binaryValue+1)); //Starts on octal equivalent
    int iter;
    if (counter%3 == 0)
    {
       iter = counter/3;
    }
    else if (counter%3 != 0)
    {
       iter = (counter/3)+1; 
    }
    c = binaryValue;
    for (int h = 0; h < iter; h++)
    {
        tempOctal = c%1000;
        int count = ceil(log10(tempOctal+1));
        tempDecimal = 0;
        for (int counterr = 0; counterr < count; counterr++)
        {
            if (tempOctal%10 != 0)
            {
                 e = pow(2.0, counterr);
                 tempDecimal += e;
            }
            tempOctal /= 10;
        }
        octalValue += (tempDecimal * pow(10.0, h));
        c /= 1000;
    }//Finished Octal conversion
    cout << i << "\t\t" << binaryValue << setw(21-counter) << octalValue << "\t\t";
    int c1, tempHex, tempDecimal1, e1, powOf;
    char letter;
    if (counter%4 == 0)//Hexadecimal equivalent
    {
       iter = counter/4;
    }
    else if (counter%4 != 0)
    {
       iter = (counter/4)+1;
    }
    c1 = binaryValue;
    for (int h = 0, g = iter-1; h < iter; h++, g--)
    {
        powOf = g*4;
        if (h == 0)
        {
              tempHex = c1 / pow(10.0, powOf);
        }
        else if (h > 0)
        {
             tempHex = c1 / pow(10.0, powOf);
             tempHex %= 10000;
        }
        int count = ceil(log10(tempHex+1));
        tempDecimal1 = 0;
        for (int counterr = 0; counterr < count; counterr++)
        {
            if (tempHex%10 != 0)
            {
                 e1 = pow(2.0, counterr);
                 tempDecimal1 += e1;
            }
            tempHex /= 10;
        }
        if (tempDecimal1 <= 9)
        {
        cout << tempDecimal1;
        }
        else if (tempDecimal1 > 9)
        {
        cout << char(tempDecimal1+55); //ASCII's numerical value for A is 65. Since 10-15 are supposed to be letters you just add 55
        }
    }
    cout << endl;
    }
}
system("pause");
return 0;
}

Any recommendations for improvement will be appreciated.

Answer 1

You have already covered 'iomanip', which infers you've already covered 'iostream'.

If that's the case, have a look at the following:

#include <iostream>
#include <iomanip>
using namespace std;

int x = 250;
cout << dec << x << " " 
     << oct << x << " "
     << hex << x << "\n"
     << x << "\n";       // This will still be in HEX

Answer 2

Break out the functions for each output type, then loop through the integer list and output each in turn by calling the function for each different format.

for (int i = 1; i <= 256; ++i)
{
  printBin(i);
  printHex(i);
  printOct(i);
}

Fundamental problem is that a function this long needs refactoring to be more modular. Imagine you are writing the code for someone else to use. How can they call your main ? How do they understand what each section of code is doing? They can't. If you make each section of code that has a particular job to do callable as a function then it's easier to understand its intent, and to reuse later.

Answer 3

Have you considered writing a general function that works with any base?

Converting a non-negative number to a generic base is simple... you just need to compute number % base and you get the least significant digit, then divide number by base and repeat to get other digits...

std::string converted_number;
do {
    int digit = number % base;
    converted_number = digits[digit] + converted_number;
    number = number / base;
} while (number != 0);

Once you have a generic conversion function then solving your problem is easy... just call it with base=2, 8 and 16 to get the results you need as strings.

Answer 4

My answer may be a bit tongue in cheek, but

 printf ("%u %o %x \n", value, value, value);

will do the trick for the octal and hexadecimal versions;)

For the binary version, i'd use a flag initialized to 256, and compare it to your number with the AND operator. If true, print a 1, if not, print a 0. Then divide the flag by two. Repeat until the flag is 1.

Pseudocode for the conversion from integer to binary

int flag = 256
do 
{
if (flag && value)
print "1"
else
print "0"
flag = flag >> 1 // aka divide by two, if my memory serves well
} while flag > 1

For the octal and hex values, i'm a bit rusty but looking around should guide you to samples you may adapt

Answer 5

Why make it any harder than it really is.

for (int i = 1; i <= 256; ++i)
{
    std::cout << std::dec << i << "\t" << std::oct << i << "\t" << std::hex << i << std::endl;
}

Answer 6

Try this

using namespace std;

template <typename T>
inline void ShiftMask(T& mask) {
    mask = (mask >> 1) & ~mask;
}

template < typename T >
std::ostream& bin(T& value, std::ostream &o)
{
    T mask = 1 << (sizeof(T) * 8 - 1);

    while (!(value & mask) && (mask != 0)) ShiftMask(mask);

    while (mask) {
        o << (value & mask ? '1' : '0');
        ShiftMask(mask);
    }

    return o;
}

int main(void) {
  for (int i=0; i<256;i++) {
    bin(a, std::cout);
    cout << " " << oct << i;
    cout << " " << dec << i;
    cout << " " << hex << i;
    cout << ""
  }
}

Answer 7

Maybe something like this?

#include "stdio.h"
int main(){
    char Chars[16]= {48,49,50,51,52,53,54,55,56,57,65,66,67,68,69,70};
    for(int n = 1;n != 256; n++)
    {
        {//decimal
            printf("%i\t", n); 
        }
        {//Hexadecimal
            char L, R;
            R = (n & 0x0F) >> 0;
            L = (n & 0xF0) >> 4;
            printf("%c%c\t", Chars[L], Chars[R]);
        }
        {//Octal
            char L, M, R;
            R = (n & 0x07) >> 0;
            M = (n & 0x38) >> 3;
            L = (n & 0xC0) >> 6;
            printf("%c%c%c\t", Chars[L], Chars[M], Chars[R]);
        }
        {//Binary
            char B0, B1, B2, B3, B4, B5, B6, B7;
            B0 = (n & 0x01) >> 0;
            B1 = (n & 0x02) >> 1;
            B2 = (n & 0x04) >> 2;
            B3 = (n & 0x08) >> 3;
            B4 = (n & 0x10) >> 4;
            B5 = (n & 0x20) >> 5;
            B6 = (n & 0x40) >> 6;
            B7 = (n & 0x80) >> 7;
            printf("%c%c%c%c%c%c%c%c\n", Chars[B0], Chars[B1], Chars[B2], Chars[B3], Chars[B4], Chars[B5], Chars[B6], Chars[B7]);
        }
        printf("256\t100\t400\t100000000\n");
    }
}