C++ Exercises: Convert a decimal number to octal number

Last update on August 14 2025 12:54:52 (UTC/GMT +8 hours)

72. Decimal to Octal Conversion

Write a C++ program to convert a decimal number to an octal number.

Visual Presentation:

C++ Exercises: Convert a decimal number to octal number

Sample Solution:-

C++ Code :

#include <iostream> // Include input/output stream library
#include <math.h>   // Include math library for mathematical functions
using namespace std; // Use the standard namespace

int main() // Main function where the execution of the program starts
{
    int dec_num, rem, quot, i = 1, j; // Declare integer variables for decimal number, remainder, quotient, and loop counters
    int oct_num[100]; // Declare an array to store octal digits, initialized to store up to 100 digits

    cout << "\n\n Convert a decimal number to octal number:\n"; // Display message prompting for decimal to octal conversion
    cout << "-----------------------------------------------\n"; // Display separator line
    cout << " Input a decimal number: "; // Prompt user to input a decimal number
    cin >> dec_num; // Read the decimal number input by the user

    quot = dec_num; // Assign the value of dec_num to quot (initializing quotient with the decimal number)
    while (quot != 0) // Loop to convert decimal number to octal
    {
        oct_num[i++] = quot % 8; // Store remainder (quotient modulo 8) as octal digit in the array
        quot = quot / 8; // Calculate next quotient by dividing it by 8 (octal base)
    }

    cout << " The octal number is: "; // Display message indicating the octal number
    for (j = i - 1; j > 0; j--) // Loop to print octal digits in reverse order
    {
        cout << oct_num[j]; // Output octal digits from the array in reverse order
    }
    cout << "\n"; // Move to the next line after printing the octal number
}

Sample Output:

 Convert a  decimal number to octal number:                            
-----------------------------------------------                        
 Input a decimal number: 15                                            
 The octal number is: 17

Flowchart:

For more Practice: Solve these Related Problems:

Write a C++ program to convert a decimal number to its octal representation using repeated division by 8.
Write a C++ program that reads a decimal number and outputs the corresponding octal number as a string.
Write a C++ program to compute the octal equivalent of a given decimal integer using a loop and modulus operator.
Write a C++ program that converts a decimal number to octal using recursive division and prints the result.

Go to:

PREV : Decimal to Hexadecimal Conversion.
NEXT : Binary to Decimal Conversion.

C++ Code Editor:

Contribute your code and comments through Disqus.