C++ Programming Code Examples C++ > Conversions Code Examples Convert Decimal Number to Octal Convert Decimal Number to Octal In this example, you will learn to convert octal number to decimal and decimal number to octal manually by creating a user-defined function. In the program, the decimal number is stored in the variable decimalNumber and passed to function decimalToOctal(). This function converts the decimal number passed by user to its equivalent octal number and returns it to main() function. #include <iostream> #include <cmath> using namespace std; int decimalToOctal(int decimalNumber); int main() { int decimalNumber; cout << "Enter a decimal number: "; cin >> decimalNumber; cout << decimalNumber << " in decimal = " << decimalToOctal(decimalNumber) << " in octal"; return 0; } // Function to convert decimal number to octal int decimalToOctal(int decimalNumber) { int rem, i = 1, octalNumber = 0; while (decimalNumber != 0) { rem = decimalNumber % 8; decimalNumber /= 8; octalNumber += rem * i; i *= 10; } return octalNumber; }