C program to convert Octal to Hexadecimal number system

Example

Input

Input octal number: 175

Output

Hexadecimal number: 7D

Logic to convert octal to hexadecimal

There is no direct conversion from octal to hexadecimal number system. You first need to convert the given octal to binary number system. Then binary number system is converted to hexadecimal number system.

Below is the step by step descriptive logic to convert octal to hexadecimal.

1. Convert the given octal number to binary number system.
2. Extract binary bits in a group of 4 bit starting from right side.
3. Write the corresponding hexadecimal of extracted 4 binary bits.

Binary to Hexadecimal conversion table

Decimal	Binary	Hexadecimal
0	0000	0
1	0001	1
2	0010	2
3	0011	3
4	0100	4
5	0101	5
6	0110	6
7	0111	7
8	1000	8
9	1001	9
10	1010	A
11	1011	B
12	1100	C
13	1101	D
14	1110	E
15	1111	F

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

#include <stdio.h>

int main()
{
    int OCTALVALUES[] = {0, 1, 10, 11, 100, 101, 110, 111};

    long long octal, tempOctal, binary, place;
    char hex[65] = "";
    int rem;

    place = 1;
    binary = 0;
    
    /* Input octal number from user */
    printf("Enter any octal number: ");
    scanf("%lld", &octal);
    tempOctal = octal;

    /*
     * Octal to binary conversion
     */
    while(tempOctal > 0)
    {
        rem = tempOctal % 10;
        binary = (OCTALVALUES[rem] * place) + binary;
        tempOctal /= 10;

        place *= 1000;
    }
    
    /* 
     * Binary to hexadecimal conversion
     */
    while(binary > 0)
    {
        rem = binary % 10000;
        switch(rem)
        {
            case 0:
                strcat(hex, "0");
                break;
            case 1:
                strcat(hex, "1");
                break;
            case 10:
                strcat(hex, "2");
                break;
            case 11:
                strcat(hex, "3");
                break;
            case 100:
                strcat(hex, "4");
                break;
            case 101:
                strcat(hex, "5");
                break;
            case 110:
                strcat(hex, "6");
                break;
            case 111:
                strcat(hex, "7");
                break;
            case 1000:
                strcat(hex, "8");
                break;
            case 1001:
                strcat(hex, "9");
                break;
            case 1010:
                strcat(hex, "A");
                break;
            case 1011:
                strcat(hex, "B");
                break;
            case 1100:
                strcat(hex, "C");
                break;
            case 1101:
                strcat(hex, "D");
                break;
            case 1110:
                strcat(hex, "E");
                break;
            case 1111:
                strcat(hex, "F");
            break;
        }

        binary /= 10000;
    }

    strrev(hex);

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

    return 0;
}

/*
Output :

Enter any octal number: 125715
Octal number: 125715
Hexadecimal number: ABCD
*/