Divide your starting decimal integer by 2. Write the answer below the starting integer and the remainder of 1, if it exists, to the right of it. As an example, we will start with the number 83. Divided by 2, it gives you a quotient of 41 with a remainder of 1.
Divide your answer from Step 1 by 2, once again placing the remainder of 1 to the right. For the above example, 41 divided by 2 equals 20 with a remainder of 1, so you would write 20 below the 41 and 1 to the right of it.
Repeat Step 2 until you are left with a quotient of 0. For our above example, the process would be as follows:
83/2 = 41 with a remainder of 1.
41/2 = 20 with a remainder of 1.
20/2 = 10 with a remainder of 0.
10/2 = 5 with a remainder of 0.
5/2 = 2 with a remainder of 1.
2/2 = 1 with a remainder of 0.
1/2 = 0 with a remainder of 1.
Assemble the remainders into a string starting with the bottom and working your way up to the top to get your decimal integer's binary equivalent. For the above example, 83 would be 1010011 in binary.