Step $1$: Start the program and initialize a loop for user input. while True: # Step $2$: Prompt the user to enter a letter in upper case. letter $=$ input$("$Enter an uppercase letter: $")$ # Step $3$: Check if the input is a valid uppercase letter. if len$($letter$)==1$ and $\text{'}$A$\text{'}<=$ letter $<=\text{'}$Z$\text{'}$: # Step $4$: Use complex conditional expressions to determine the corresponding digit. if letter in 'ABC': digit $=2$ elif letter