Change your force = mass * acceleration program into a program that uses functions.
In addition, allow the user to repeat the calculation as many times as desired.

For example, your main pseudocode would have these simple parts:


variable declaration
while the user wishes to continue, do the following:
    a function call to the input function
    a function call to the calculate force function
    a function call to the output function


For the most part, many programs can be written this way. 
Which is: get input, do calculations and then perform output.
Be sure to implement your code modularly and not all at once.
In other words, write your output function first and then save,
compile, and execute. Then, implement the next small piece and
repeat this process. It is much easier to write code in this 
manner rather than attempting to write it all perfectly and 
compiling at the very end (with possibly many errors rather 
than only a couple).