C++ Program to Convert Decimal to Octal

In this article, you will learn and get code on decimal to octal conversion in C++. The program is created with and without using the modulo operator. Also, with and without the use of a user-defined function.

But before going through the program, if you are not aware of the steps and logic used behind the conversion, refer to Decimal to Octal.

Decimal to Octal in C++

To convert a decimal number to an octal number in C++ programming, you have to ask the user to enter the decimal number first. and then convert it into its equivalent octal value as shown in the program given below:

#include<iostream>
using namespace std;
int main()
{
    int decimalNum, octalNum[50], i=0;
    cout<<"Enter any Decimal number: ";
    cin>>decimalNum;
    while(decimalNum != 0)
    {
        octalNum[i] = decimalNum%8;
        i++;
        decimalNum = decimalNum/8;
    }
    cout<<"\nEquivalent Octal Value = ";
    for(i=(i-1); i>=0; i--)
        cout<<octalNum[i];
    cout<<endl;
    return 0;
}

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

C++ program convert decimal to octal

Now, enter any decimal number, such as 358, and press the ENTER key to see its equivalent octal value, as shown in the screenshot below:

decimal to octal c++

The following is a dry run of the above program with a decimal number input, say 358:

Decimal to octal conversion in C++ without using the modulo operator

This program does not use the modulo operator (%) while converting a decimal number to octal.

#include<iostream>
using namespace std;
int main()
{
    int decimalNum, octalNum[50], i=0, temp, chk, rem;
    cout<<"Enter any Decimal number: ";
    cin>>decimalNum;
    while(decimalNum!=0)
    {
        temp = decimalNum/8;
        chk = temp*8;
        rem = decimalNum - chk;
        octalNum[i] = rem;
        i++;
        decimalNum = temp;
    }
    cout<<"\nEquivalent Octal Value = ";
    for(i=(i-1); i>=0; i--)
        cout<<octalNum[i];
    cout<<endl;
    return 0;
}

It will produce the same output as the previous program.

Decimal to octal conversion in C++ using a user-defined function

This is the last program that uses the user-defined function DecimalToOctal(). It takes a decimal number as its argument and converts it into its equivalent octal value.

#include<iostream>
using namespace std;
void DecimalToOctal(int);
int octalNum[50];
static int i;
int main()
{
    int decimalNum;
    cout<<"Enter any Decimal number: ";
    cin>>decimalNum;
    DecimalToOctal(decimalNum);
    cout<<"\nEquivalent Octal Value = ";
    for(i=(i-1); i>=0; i--)
        cout<<octalNum[i];
    cout<<endl;
    return 0;
}
void DecimalToOctal(int decimalNum)
{
    while(decimalNum != 0)
    {
        octalNum[i] = decimalNum%8;
        i++;
        decimalNum = decimalNum/8;
    }
}

This program has the same output as the first program in this article.

Note: A static int type variable initializes its initial value as 0, automatically.

The same program in different languages

C++ Quiz


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