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C++ Program to Convert Octal to Binary

In this article, you will learn and get code for octal to binary conversion in C++. The first program is created that actually converts and then prints the binary equivalent of an octal number. The second program simply prints the binary equivalent of each octal digit one by one.

Before going through these programs, if you're not aware of the simple steps and formula used for the conversion, you can refer to the octal to binary formula to get all the things you need.

There are two approaches that can be used to create a program for octal to binary conversion in C++:

  1. Octal to Binary Direct Conversion.
  2. Octal to Binary Indirect Conversion.

In indirect conversion, convert the given octal number into its equivalent decimal value first and then convert the decimal to its equivalent binary value. But here, the program is created using direct conversion only. Because you have the ability to approach indirect conversion with yourself. The program for an indirect approach is already given in a separate article.

Octal to Binary in C++

To convert an octal number to a binary number in C++ programming, you have to ask the user to enter the octal number and then convert it into its equivalent binary number. And finally, display the binary value on the output as shown in the program given below.

The question is: write a program in C++ that converts octal to binary. The answer to this question is given below:

#include<iostream>
#include<string.h>
using namespace std;
int main()
{
    int octalNum, rev=0, rem, chk=0;
    char binaryNum[40] = "";
    cout<<"Enter the Octal Number: ";
    cin>>octalNum;
    while(octalNum!=0)
    {
        rem = octalNum%10;
        if(rem>7)
        {
            chk++;
            break;
        }
        rev = (rev*10) + rem;
        octalNum = octalNum/10;
    }
    if(chk==0)
    {
        octalNum = rev;
        cout<<"\nEquivalent Binary Value: ";
        while(octalNum!=0)
        {
            rem = octalNum%10;
            switch(rem)
            {
                case 0: strcat(binaryNum, "000");
                    break;
                case 1: strcat(binaryNum, "001");
                    break;
                case 2: strcat(binaryNum, "010");
                    break;
                case 3: strcat(binaryNum, "011");
                    break;
                case 4: strcat(binaryNum, "100");
                    break;
                case 5: strcat(binaryNum, "101");
                    break;
                case 6: strcat(binaryNum, "110");
                    break;
                case 7: strcat(binaryNum, "111");
                    break;
            }
            octalNum = octalNum/10;
        }
        cout<<binaryNum;
    }
    else
        cout<<"\nInvalid Octal Digit!";
    cout<<endl;
    return 0;
}

This program was built and runs under the Code::Blocks IDE. Here is its sample run:

C++ program convert octal to binary

Now supply any octal number, say 364, as input and then press the ENTER key to convert and print its binary equivalent as shown in the output given below:

octal to binary c++

The function strcat() is used to concatenate strings. It takes two strings as its argument. The value of the second string gets appended at the end of the first string.

The following block of code is included in the above program:

while(octalNum!=0)
{
    rem = octalNum%10;
    if(rem>7)
    {
        chk++;
        break;
    }
    rev = (rev*10) + rem;
    octalNum = octalNum/10;
}

is used to check whether any digit of a given octal number is greater than 7 or not. If any digit is found to be greater than 7, then that digit is not a valid octal digit. Because an octal number can only have eight digits (ranging from 0 to 7),

The while loop executes in the following ways (supposing user input as 364):

So the dry run of the above program with user input 364 goes like this: (Inside the if block):

In C++, print the binary equivalent of an octal number

Now let's create another program that only prints the binary equivalent of an octal number given by the user at run-time without actually converting it.

#include<iostream>
using namespace std;
int main()
{
    int octalNum, rev=0, rem;
    cout<<"Enter the Octal Number: ";
    cin>>octalNum;
    while(octalNum!=0)
    {
        rem = octalNum%10;
        rev = (rev*10) + rem;
        octalNum = octalNum/10;
    }
    octalNum = rev;
    cout<<"\nEquivalent Binary Value: ";
    while(octalNum!=0)
    {
        rem = octalNum%10;
        switch(rem)
        {
            case 0: cout<<"000";
                break;
            case 1: cout<<"001";
                break;
            case 2: cout<<"010";
                break;
            case 3: cout<<"011";
                break;
            case 4: cout<<"100";
                break;
            case 5: cout<<"101";
                break;
            case 6: cout<<"110";
                break;
            case 7: cout<<"111";
                break;
            default: cout<<"--InvalidOctalDigit("<<rem<<")--";
                break;
        }
        octalNum = octalNum/10;
    }
    cout<<endl;
    return 0;
}

Here is its sample run with user input 254 (an octal number):

octal to binary program c++

If the user enters an octal number that contains one or more invalid octal digits, say 2948, Then here is the output you'll see:

c++ program octal to binary

The same program in different languages

C++ Quiz

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