[算法练习] 正整数数制转换

题目说明：

把一个十进制的正整数转换成N进制的数，或者把一个N进制的数转换成十进制的数（2 <= N,M <=16）。

还可以继续扩展到负数和小数进制转换算法。

程序代码：

#include <gtest/gtest.h>
using namespace std;

string DecimalConvertToRadix(int nValue, int nRadix)
{
    int State[256] = {0};
    int nIndex = 0;
    static char szText[] = "0123456789ABCDEF";

    while (nValue)
    {
        State[nIndex++] = nValue % nRadix;
        nValue = nValue / nRadix;
    };

    string strValue;
    for (int i = nIndex-1; i >= 0; --i)
    {
        strValue += szText[State[i]];
    }

    if (strValue.empty())
    {
        strValue = "0";
    }

    return strValue;
}

int RadixConvertToDecimal(const string& strValue, int nRadix)
{
    int nValue = 0;
    int Base = 1;    

    for (int i = strValue.size()-1; i >=0; i--)
    {
        char cTemp = strValue[i];
        if (cTemp >= ‘a‘ && cTemp <= ‘f‘)
        {
            nValue += (cTemp - ‘a‘ + 10) * Base;
        }
        else if (cTemp >= ‘A‘ && cTemp <= ‘F‘)
        {
            nValue += (cTemp - ‘A‘ + 10) * Base;
        }
        else
        {
            nValue+= (cTemp - ‘0‘) * Base;
        }

        Base *= nRadix;
    }

    return nValue;
}

TEST(Pratices, tNumberConversion)
{
    // 10进制转2进制
    // 0 =>
    // 1 => 1
    // 2 => 10
    // 34 => 100010
    // 100 => 1100100
    ASSERT_EQ(DecimalConvertToRadix(0, 2), "0");
    ASSERT_EQ(DecimalConvertToRadix(1, 2), "1");
    ASSERT_EQ(DecimalConvertToRadix(2, 2), "10");
    ASSERT_EQ(DecimalConvertToRadix(34, 2), "100010");
    ASSERT_EQ(DecimalConvertToRadix(100, 2), "1100100");

    // 10进制转8进制
    // 0 =>
    // 7 => 7
    // 8 => 10
    // 9 => 11
    // 34 => 42
    // 100 => 144
    ASSERT_EQ(DecimalConvertToRadix(0, 8),"0");
    ASSERT_EQ(DecimalConvertToRadix(7, 8),"7");
    ASSERT_EQ(DecimalConvertToRadix(8, 8),"10");
    ASSERT_EQ(DecimalConvertToRadix(9, 8),"11");
    ASSERT_EQ(DecimalConvertToRadix(34, 8),"42");
    ASSERT_EQ(DecimalConvertToRadix(100, 8),"144");

    // 2进制转10进制
    // 0 = > 0
    // 1 = > 1
    // 10 = > 2
    // 1101 = >13
    // 11111111 => 255
    ASSERT_EQ(RadixConvertToDecimal("0", 2),0);
    ASSERT_EQ(RadixConvertToDecimal("1", 2),1);
    ASSERT_EQ(RadixConvertToDecimal("10", 2),2);
    ASSERT_EQ(RadixConvertToDecimal("1101", 2),13);
    ASSERT_EQ(RadixConvertToDecimal("11111111", 2),255);

    // 16进制转换10进制
    // 0 => 0
    // f => 15
    // 10 => 16
    // 1Fea => 8170
    // FFFF => 65535
    ASSERT_EQ(RadixConvertToDecimal("0", 16),0);
    ASSERT_EQ(RadixConvertToDecimal("f", 16),15);
    ASSERT_EQ(RadixConvertToDecimal("10", 16),16);
    ASSERT_EQ(RadixConvertToDecimal("1Fea", 16),8170);
    ASSERT_EQ(RadixConvertToDecimal("FFFF", 16),65535);
}

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