Modular programming is the method of programming small task or sub-programs that can be arranged in multiple variations to perform desired results. This methodology is great for preventing errors due to the fact that each task executes a specific process and can be debugged individually or within a larger program when combined with other tasks or sub programs.

C# is a great example of how to implement modular programming because it allows for functions, methods, classes and objects to be use to create smaller sub programs. A program can be built from smaller pieces of code which saves development time and reduces the chance of errors because it is easier to test a small class or function for a simple solutions compared to testing a full program which has layers and layers of small programs working together.
Yes, it is possible to write the same program using modular and non modular programming, but it is not recommend it.

When you deal with non modular programs, they tend to contain a lot of spaghetti code which can be a pain to develop and not to mention debug especially if you did not write the code. In addition, in my experience they seem to have a lot more hidden bugs which waste debugging and development time.

Modular programming methodology in comparision to non-mondular should be used when ever possible due to the use of small components. These small components allow business logic to be reused and is easier to maintain.

From the user’s view point, they cannot really tell if the code is modular or not with today’s computers.