C program to convert Octal to Binary number system

Write a C program to read 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 program.

Input octal number: 172

Binary of 172: 01111010

Required knowledge

Basic C programming, For loop

Additional programming knowledge required for this program.

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.

Algorithm to convert octal to binary

Like binary to octal conversion, I have divided the octal to binary conversion in three steps:

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

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

/**
 * 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;
} 

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

Happy coding ;)