HW8: Separate Compilation 


Write three simple C source files:

promptint.c:
	contains a single function, promptint(), that receives
	three arguments:
		a FILE * parameter that refers to an i/o stream
			that is ALREADY open for reading
		a FILE * parameter that refers to an i/o stream
			that is ALREADY open for writing or is 
			equal to NULL
		a string that will serve as a prompt
	An integer value is always returned.

	First, promptint() checks whether the second
		FILE * parameter is equal to NULL (NULL is defined
		in the stdio library, so be sure to include it
		in the function file). If the FILE * parameter is
		not equal to NULL, then the third parameter (the 
		string) is written to the i/o stream given by
		the second parameter.  Second, even if the
		second parameter is NULL, an integer is read 
		from the i/o stream given by the first FILE *
		parameter and this integer is returned.

	sample usage: 

		int val;
		val = promptint(stdin,stdout,"Type an integer");

	interpretation - "Type an integer" is written to stdout
		and an integer is read from stdin.  That integer
		is returned and stored in val.

putint.c:
	contains a single function, putint(), that recieves three
	arguments:
		a FILE * parameter that refers to an i/o stream
			that is ALREADY open for writing
		a string that serves as a label
		an integer
	An integer is returned.

	putint() writes the string followed by the integer
		(followed by \n) to the indicated i/o stream 
		(the first argument).  putint() returns the 
		number that it printed out.
	
	Sample usage:
		int val1,val2;
		val2=3;
		val1 =putint(stdout,"The value is ",val2);

	The output written to stdout would be:
The value is 3
 
The value 3 is returned and stored in val1.

simplesum.c:
	contains a single function, main(), that calls promptint()
		twice, each time passing it stdin and stderr as
		its FILE * arguments.  It then uses putint()
		to print out the sum of the integers returned by 
		promptint() to stdout. The output of this program
		is a single line of the form: "SUM = x"
		where "x" is the sum of the integers returned 
		by promptint().

Note: that promptint.c and putint.c are not complete programs, they 
	are merely files that define particular functions.

Besides writing these three files, you are to compile them separately,
using the "-c" option in the acc command:

	acc -c promptint.c


This will produce a ".o" file .  Then produce an executable file 
from the three object files (the ".o" files):

	acc promptint.o putint.o simplesum.o

BEFORE YOU WRITE YOUR CODE:
	Read the specs above carefully to make sure you understand
	exactly what is being called for.

BEFORE YOUR SUBMIT YOUR CODE:
	Test your code very CAREFULLY. You may want to make variations 
	of simplesum.c in order to test promptint() and putint().


SUBMITTING YOUR HOMEWORK:

	toteach 8 promptint.c promptint.o putint.c putint.o simplesum.c simplesum.o a.out