C program to evaluate the 1st derivative of a function at any given point

Writing C programs for numerical differentiation is interesting and fun. Here is one that I wrote years back. Enjoy!

C program to evaluate the 1st derivative of a function at any given point
C program to evaluate the 1st derivative of a function at any given point
C program to evaluate the 1st derivative of a function at any given point
C program to evaluate the 1st derivative of a function at any given point
C program to evaluate the 1st derivative of a function at any given point
C program to evaluate the 1st derivative of a function at any given point