# Decimal to Octal conversion in C++

This tutorial would help in learning the following:

**Conversion of numbers**from decimal-system (using 0 to 9) to octal-system (using 0 to 7).**Conversion of characters**into their respective ASCII codes.- Code for
**Decimal to Octal conversion in C++.**

## Convert Decimal to Octal in C++

The decimal number system uses 10 digits (0 to 9) to represent a number while the octal number system uses 7 digits (0 to 7). The following algorithm is used to convert a decimal-number into an octal-number:

*let the number be 63*

- divide the number by 8 (integer division) and note down the remainder and keep the quotient

*63/8: quotient -> 7, remainder -> 7* - repeat step 1 on the quotient till there comes another quotient which is 0, note down the remainders obtained in right-to-left fashion

*7/8: quotient -> 0, remainder -> 7; remainder-list -> 77*

- the remainders, placed in the right-to-left fashion form the binary representation

*(63)*_{10}~ (77)_{8}

Each character used in computing is assigned a **special ASCII code** (decimal-number-system); hence, to convert a character into octal-form, its ASCII code can be obtained and it can be converted.

*Note, there can be different encoding systems on different machines*.

### CPP Program to convert decimal to octal

#include <stdio.h> #define string "Code Speedy" //this value can be changed to obtain the octal code for any collection of characters #define number 63//this value can be changed to obtain the octal form of any non negative integer void stringToOctal(char *); int octal(int); int main() { char *p=string; printf("The octal form of %d is %d\n",number,octal(number)); printf("The octal equivalent of %s is:\n",string); stringToOctal(p); return 0; } void stringToOctal(char *p)//converts a line to binary code { char c;//characters can be treated as integers in C++ while((c=*(p++))!='\0'){//each character is extracted and its binary code is printed printf("%d.",octal(c));//a full-stop follows after each individual binary code } printf("\n"); } int octal(int x)//converts an integer to its equivalent binary form { if(x<=1)return x; else return (x%8) + 10*octal(x/8); }

#### Output:

The octal form of 63 is 77 The octal equivalent of Code Speedy is: 103.157.144.145.40.123.160.145.145.144.171.

## Summary:

**int octal(int):**

- a recursive approach is taken.
- a remainder (x%8) is taken at each call and added next to the remainder of the next call.
- multiplication with 10 is done to ensure that the addition is done in right-to-left fashion and not simple summation.

**void stringToOctal(char *):**

- a pointer to a collection of characters is taken as parameter.
- as long as the pointer does not point to a null character, the octal form of the current character is printed.

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