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How To Use Base-8 (Octal) Numbers In Modern C++?

How To Use Base 8 Octal Numbers In Modern C++

In general, in nearly all programming languages, including Modern C++, we use base-10 numbers, while our computer hardware uses the binary base-2 system (bits). I personally believe that base-10 is because we typically have 10 fingers and since we learn to counting on our fingers we use base-10 primarily. However, due to the way binary works it is sometimes convenient to use base-8 system octal (oct) and base-16 system hexadecimal (hex) numbers in programming. In this post, we explain how to use Base-8 octal numbers in Modern C++.

What is the octal number system?

The octal – or oct – number system is the base-8 system, Octal uses the digits from 0 to 7. In general, we use a base-10 number system in normal life. In the digital world we also use base-2, base-8, and base-16 as well as base-10. If you want to explore the different numbering systems, try this Wikipedia article.

Let’s give some octal examples and their values in the decimal system,

  • 1octal  = 1
  • 10octal  = 8
  • 100octal = 64

How to declare base-8 (octal) number in modern C++?

In C++, when we use octal numbers in C++ code, we put 0 on the left side of an octal number. This zero shows it is an octal representation.

How to initialize base-8 (octal) number in modern C++?

here the first zero on the left side of 0010 defines this number representation is an octal representation. The integer x value is results as 8;

How to set an integer to base-8 (octal) number in modern C++?

We can use std::istringstream() which is declared in <sstream> library. Here Octal number “010” is declared into x as a octal number, now when you print this variable, it will be displayed in octal decimal system,

How to print out base-8 (octal) number in modern C++?

When we print out base-8 (octal) numbers we use std::oct format as below,

How to print out base-8 (octal) number in C language?

C has very powerful printf() function and there is a ‘%oFormat Specifier to print out octal numbers.

How to display base-8 (octal) number in C++ Builder?

C++ Builder is using UnicodeString in most of components, and UnicodeString very powerful printf() method. There is a ‘%oFormat Specifier to print out octal numbers that can be used as below,

How to convert base-8 (octal) number to (base-10) decimal number in modern C++?

When you declare an integer with octal representation, it is automatically converted to base-10 number. For example:

here a = 8 in the decimal system.

there is another method std::stoi that converts octal representation in string to an integer. Here is an example,

How to convert (base-10) decimal number to base-8 (octal) number in modern C++?

In C++, computation is done in base-2 while you have a decimal number. If you want to convert base-10 decimal number to base-8 octal number, you only need to convert to a octal number or string when you want to display. Here is how you can do:

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About author

Dr. Yilmaz Yoru has 35+ years of coding with more than 30+ programming languages, mostly C++ on Windows, Android, Mac-OS, iOS, Linux, and some other operating systems. He was born in 1974, Eskisehir-Turkey, started coding in college and graduated from the department of Mechanical Engineering of Eskisehir Osmangazi University in 1997. He worked as a research assistant at the same university for more than 10 years. He received his MSc and PhD degrees from the same department at the same university. Since 2012, he is the founder and CEO of Esenja LLC Company. He has married and he is a father of a son. Some of his interests are Programming, Thermodynamics, Fluid Mechanics, Artificial Intelligence, 2D & 3D Designs, and high-end innovations.
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