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Hexadecimal to Octal

S
/* C program to convert Hexadecimal to Octal number system */

#include <stdio.h>

int main()
{
#define MAX_STR_LEN 17
    char hex[MAX_STR_LEN];
    long long octal, bin, place;
    int i = 0, rem, val;

    /* Input hexadecimal number from user */
    printf("Enter any hexadecimal number: ");
    fgets(hex, MAX_STR_LEN, stdin);

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

    /* Hexadecimal to binary conversion */
    for (i = 0; hex[i] != '\0'; 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.");
        }

        place = 10000;
    }

    place = 1;

    /* Binary to octal conversion */
    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;
}