C++ Program to convert Decimal to Binary We can convert any decimal number (base-10 (0 to 9)) into binary number (base-2 (0 or 1)) by C++ program. Decimal Number Decimal number is a base 10 number because it ranges from 0 to 9, there are total 10 digits between 0 to 9. Any combination of digits is decimal number such as 223, 585, 192, 0, 7 etc. Binary Number Binary number is a base 2 number because it is either 0 or 1. Any combination of 0 and 1 is binary number such as 1001, 101, 11111, 101010 etc.