C++ Program to Convert Octal Number to Binary Number

In a computer system, the binary number is expressed in the binary numeral system while the octal number is in the octal numeral system. The binary number is in base 2 while the octal number is in base 8.

Here, we provide the tabular data to understand binary numbers and their corresponding octal numbers as follows:

• Using stoi() and bitset
• Digit-wise mapping
• Using lookup table

Octal to Binary Conversion Using stoi() and bitset

In C++, both stoi() and bitset are used to work with numeric conversion and binary representation.

• stoi: This is used for string number conversion.
• bitset: This is used for bit manipulation.

Syntax

Its syntax is as follows:

int num = stoi(octal_str, nullptr, 8);
string bin = bitset<16>(num).to_string();

Example

In this example, we converts the octal value "17" to decimal (15) and then displays it as an 8-bit binary number.

#include <iostream>
#include <bitset>
#include <string>

using namespace std;

int main() {
   string octal = "17";
   int num = stoi(octal, nullptr, 8);
   string binary = bitset<8>(num).to_string();
   cout << "The Binary result is " << binary;
   return 0;
}

Output

The above program obtained the following result:

The Binary result is 00011111

Octal to Binary Conversion Using Digit-wise Mapping

In this approach, each octal digit is individually mapped to a 3-digit binary equivalent using a switch-case structure.

Example

Here, each character of octal string is matched and replaced with 3-bit binary string.

#include <iostream>
#include <string>

using namespace std;

int main() {
   string octal = "25";
   string binary = "";

   for (char digit : octal) {
      switch (digit) {
         case '0': binary += "000"; break;
         case '1': binary += "001"; break;
         case '2': binary += "010"; break;
         case '3': binary += "011"; break;
         case '4': binary += "100"; break;
         case '5': binary += "101"; break;
         case '6': binary += "110"; break;
         case '7': binary += "111"; break;
      }
   }

   cout << "The Binary result is " << binary;
   return 0;
}

Output

The above code obtained the following output:

The Binary result is 010101

Octal to Binary Conversion Using Lookup Table

This approach explain about mapping using a lookup array that convert each octal digit into binary form.

Example

This example shows the usage of lookup table under the for loop.

#include <iostream>
#include <string>

using namespace std;

int main() {
   string octal = "73";
   string lookup[] = {"000", "001", "010", "011", "100", "101", "110", "111"};
   string binary = "";

   for (char digit : octal) {
      binary += lookup[digit - '0'];
   }

   cout << "The Binary result is " << binary;
   return 0;
}

Output

The above code produces the following output:

The Binary result is 111011