十六进制转换成八进制的两种方法

1、十六进制转换成八进制【方法一】

#include <stdio.h>
#define MAX_STR_LEN 17

int main()
{
    char hex[MAX_STR_LEN];
    long long octal, bin, place;
    int i = 0, rem, val;

    /*用户输入十六进制数*/
    printf("Enter any hexadecimal number: ");
    fgets(hex, MAX_STR_LEN, stdin);

    octal = 0ll;
    bin = 0ll;
    place = 0ll;

    /*十六进制--->二进制*/
    for (i = 0; hex[i] != '\n'; i++)
    {
        bin = bin * place;

        switch (hex[i])
        {
        case '0':
            bin += 0;
            break;
        case '1':
            bin += 1;
            break;
        case '2':
            bin += 10;
            break;
        case '3':
            bin += 11;
            break;
        case '4':
            bin += 100;
            break;
        case '5':
            bin += 101;
            break;
        case '6':
            bin += 110;
            break;
        case '7':
            bin += 111;
            break;
        case '8':
            bin += 1000;
            break;
        case '9':
            bin += 1001;
            break;
        case 'a':
        case 'A':
            bin += 1010;
            break;
        case 'b':
        case 'B':
            bin += 1011;
            break;
        case 'c':
        case 'C':
            bin += 1100;
            break;
        case 'd':
        case 'D':
            bin += 1101;
            break;
        case 'e':
        case 'E':
            bin += 1110;
            break;
        case 'f':
        case 'F':
            bin += 1111;
            break;
        default:
            printf("Invalid hexadecimal input.");
            break;
        }

        place = 10000;
    }

    place = 1;

    /*二进制--->八进制*/
    while (bin > 0)
    {
        rem = bin % 1000;

        switch (rem)
        {
        case 0:
            val = 0;
            break;
        case 1:
            val = 1;
            break;
        case 10:
            val = 2;
            break;
        case 11:
            val = 3;
            break;
        case 100:
            val = 4;
            break;
        case 101:
            val = 5;
            break;
        case 110:
            val = 6;
            break;
        case 111:
            val = 7;
            break;
        }

        octal = (val * place) + octal;
        bin /= 1000;

        place *= 10;
    }

    printf("Hexadecimal number = %s\n", hex);
    printf("Octal number = %lld", octal);

    return 0;
}

测试结果：

Enter any hexadecimal number: acb
hex[0]:a
hex[1]:c
hex[2]:b
Hexadecimal number = acb

Octal number = 5313

2、十六进制转换成八进制【方法二】

#include <stdio.h>
#include <string.h>

const char *hex_to_oct(const char *hex)
{
    #define MAX_OCT_STR_LEN 23
    static char octal[MAX_OCT_STR_LEN];
    memset(octal, '\0', MAX_OCT_STR_LEN); 

    unsigned long long decimal = 0;
    int i = 0;
    int len;

    if (hex == NULL)
    {
        return octal;
    }

    /*十六进制--->十进制*/
    while (*hex != '\n' && *hex != '\0')
    {
        char ch = *hex;

        if (ch >= '0' && ch <= '9')
        {
            ch -= '0';
        }
        else if (ch >= 'a' && ch <= 'f')
        {
            ch = ch - 'a' + 10;
        }
        else if (ch >= 'A' && ch <= 'F')
        {
            ch = ch - 'A' + 10;
        }
        else
        {
            printf("Invalid hexadecimal input: %c\n", ch);
            break;
        }

        decimal *= 16;
        decimal += ch;
        hex++;
    }

    /*十进制--->八进制*/
    if (decimal == 0)
    {
        octal[0] = '0';
        len = 1;
    }
    else
    {
        i = 0;
        while (decimal > 0)
        {
            octal[i] = '0' + decimal % 8;
            i++;
            decimal /= 8;
        }

        len = i;
    }

    octal[len] = '\0';

    /*转换八进制字符串*/
    for (i = 0; i < len / 2; i++)
    {
        char tmp = octal[i];
        octal[i] = octal[len - i - 1];
        octal[len - i - 1] = tmp;
    }

    return octal;
}

int main()
{
    #define MAX_HEX_STR_LEN 17
    char hex[MAX_HEX_STR_LEN];

    /*输入十六进制数*/
    printf("Enter any hexadecimal number: ");
    fgets(hex, MAX_HEX_STR_LEN, stdin);

    const char *octal = hex_to_oct(hex);

    printf("Hexadecimal number = %s\n", hex);
    printf("Octal number = %s\n", octal);

    return 0;
}

测试结果：

Enter any hexadecimal number: acb
Hexadecimal number = acb

Octal number = 5313

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