click the green flag to start using the calculator this is an even simpler version that I created ... https://scratch.mit.edu/projects/42436686
I've used a variable (output) to display the result of each calculation instead of building an array of 7-segment display which can complicate the code. After each calculation you can continue to calculate with the final result of the previous stage e.g. 8x8=64 64/4=16 etc. If you want to start from scratch click on the green C (clear) button
