main(int argc, char** argv)
(The syntax char** argv declares argv to be a pointer to a pointer to a character, that is, a pointer to a character array (a character string)--in other words, an array of character strings. You could also write this as char* argv[]. Don't worry too much about the details of the syntax, however--the use of the array will be made clearer below.)
When you run a program, the array argv contains, in order, all the information on the command line when you entered the command (strings are delineated by whitespace), including the command itself. The integer argcgives the total number of strings, and is therefore equal to equal to the number of arguments plus one. For example, if you typed
a.out -i 2 -g -x 3 4
the program would receive argc = 7
argv[0] = "a.out"
argv[1] = "-i"
argv[2] = "2"
argv[3] = "-g"
argv[4] = "-x"
argv[5] = "3"
argv[6] = "4"
tips,
up to a certain approximation. This is one such example where a continuous computation can be approximated using discrete formulation. The key here is the value of 
which should be chosen NOT too large (such that curvatures are totally avoided) nor too small (such that IEEE754 might fail to represent using the system hardware). Now, one can easily write off a C/Java program so as to calculate the differentiation of a function at a given value.