This paper demonstrates that genetic programming can be used to create a circuit-constructing computer program that contains both conditional operations and inputs (free variables). The conditional operations and free variables enable a single genetically evolved program to yield functionally and topologically different electrical circuits. The conditional operations can trigger the execution of alternative sequences of steps based on the particular values of the free variables. The particular values of the free variables can also determine the component value of the circuit's components. Thus, a single evolved computer program can represent the solution to many instances of a problem. This principle is illustrated by evolving a single computer program that yields a lowpass or a highpass filter whose passband and stopband boundaries depend on the program's inputs.