This program will solve the zeros for a function in the form ax^3+bx^2+cx+d=0 using the cubic formula.
When you start the program if you havent already input the values of a,b,c,d. press 1 and input the numbers,
then you can press 2 and solve it, and you can see the values of each x if you press 3 when at the main
screen. ive updated the graph function now so it shows all the zeros and all the peaks of the function.