Professor Puckett, inventor of Max and PureData (the two top visual programming languages for DSP) has a book, The Theory and Practice of Electronic Music, with interactive examples written in PD, this one probably has an example exercise for a pitch shifter [0]

I often recommend also Music and Computers originally out of Columbia. [1]

[0]http://msp.ucsd.edu/techniques.htm

[1]https://musicandcomputersbook.com/