C program to convert Octal to Binary number system

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

Example

Input

Input octal number: 172

Output

Binary of 172: 01111010

Required knowledge

Basic C programming, While loop, Array

Octal number system

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

Binary number system

Binary number system is a base 2 number system. It uses only two symbols i.e. 0 and 1 to represent all numbers.

Logic to convert octal to binary number system

I have divided the octal to binary conversion in three steps.

Extract last digit from octal number.
Find binary equivalent of octal digit found above.
Combine all converted binary together.

Octal to Binary conversion

Octal to Binary conversion table

Decimal	Octal	Binary
0	0	000
1	1	001
2	2	010
3	3	011
4	4	100
5	5	101
6	6	110
7	7	111

Algorithm to convert octal to binary

Algorithm Conversion from Octal to Binary
begin:
    read(octal);
    OCTALVALUES[] ← 0, 1, 10, 11, 100, 101, 110, 111;
    binary ← 0; rem ← 0; place ← 1;
    While(octal > 0)
    begin:
        rem ← octal % 10;
        binary ← (OCTALVALUES[rem] * place) + binary;
        octal ← octal / 10;
        place ← place * 1000;
    end;
    write('Binary =' binary);
end;

Program to convert octal to binary number system

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

#include <stdio.h>

int main()
{
    int OCTALVALUES[] = {0, 1, 10, 11, 100, 101, 110, 111};
    long long octal, tempOctal, binary, place;
    int rem;
    
    /* Input Octal number from user */
    printf("Enter any Octal number: ");
    scanf("%lld", &octal);
    tempOctal = octal;

    binary = 0;
    place  = 1;
    
    /* Convert octal to binary */
    while(tempOctal > 0)
    {
        /* Extract the last digit of octal */
        rem = tempOctal % 10;

        /*
         * Get the binary equivalent of octal digit
         * add it to the binary variable
         */
        binary = (OCTALVALUES[rem] * place) + binary;

        /* Remove the last octal digit */
        tempOctal /= 10;

        /* Increase the place value */
        place *= 1000;
    }

    printf("Octal number = %lld\n", octal);
    printf("Binary number = %lld", binary);

    return 0;
}

Output

Enter any Octal number: 1720
Octal number = 1720
Binary number = 1111010000

Happy coding 😉