C program to convert Octal to Hexadecimal number system

Write a C program to input octal number from user and convert to hexadecimal number system. How to convert from octal number system to hexadecimal number system in C program. Logic to convert octal to hexadecimal number system in C programming.

Example

Input

Input octal number: 175

Output

Hexadecimal number: 7D

Required knowledge

Basic C programming, Switch…case statement, While loop, Array

Must know –
Program to find last digit of a number.
Program to convert octal to binary.
Program to convert binary to hexadecimal.

Octal number system

Octal number system is a base 8 number system. It uses 8 symbols to represent all its numbers i.e. 01234567

Hexadecimal number system

Hexadecimal number system is a base 16 number system. It uses 16 symbols to represent all its numbers i.e. 0123456789ABCDEF

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.

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

Octal to Hexadecimal conversion

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

Program to convert octal to hexadecimal

/**
 * 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

Happy coding 😉