Pipes for Process Communication

Exercise. Write a C program factorial.c that calculates the factorial of a positive number given as an argument in the command line, and prints out the answer. Execution example:

        bash$ factorial 50   
        30414093201713378043612608166064768844377615689605120

This is easy to code, except that the product 1*2*3* ... *50 is much too large for an int or a long in C. However, there is a neat program called bc that handles any size integers. Try the following:

	
        bash$ bc
              1*2*3*4*5*6*7*8*9*10*11*12*13*14*15
        1307674368000
        quit
        bash$

User input is marked in italic. Using pipes, we can use bc from inside our factorial program. Your program should:

Create a pipe
fork/exec the bc program with its stdin redirected to the read end of pipe
Parent writes 1*2*3*...*50\n (or whatever the number argument is) to the write end of the pipe
Child reads that, computes, and writes its answer to stdout
Parent writes quit\n to the write end of the pipe
Child reads that and terminates
Parent waits for the child to terminate, then terminates itself