Transistor Calculator

This is a calculator I built that performs four-bit addition and multiplication. The switch in the middle of the input areas controls between multiplication and addition.

The addition is done with four full adders.

The multiplication uses D-Flip-Flops to store the result of the multiplicand being added to the previous addition result. The multiplier informs the clock how many times to pulse. It does that by using D-Flip-Flops, adders, and NAND gates. Once the value stored in the Flip-Flops equals that of the multiplier, it disables the clock.