To convert the functionality from Chapter 5 and 6 using user defined functions, we need to identify the independent tasks and create separate functions for each.

First, for the SMIS system, we can create functions for each menu option. For example, a function to accept student details, another to display details, and one to calculate attendance percentage. Each function should accept required parameters and return the calculated values.

Second, for calculations like tent design from Chapter 6, we can create functions such as con(l, r) for cone calculations and post_tax_price(cost) for tax calculations. These functions can be reused when the company designs new products.

Third, by using functions, the program becomes more organised and easier to read. The code length is reduced as the same code is not written at multiple places. This makes debugging easier.

Fourth, functions allow modularity where work can be divided among team members and completed in parallel. Each member can work on different functions independently.

Finally, the main program will simply call these functions by passing appropriate parameters, making the code cleaner and more maintainable compared to writing all logic in one place.