This set of programs is intended to demonstrate the several ways that file input/output can be integrated into a C program.
D. House, 9/23/2019, Clemson University

gennumbers generates pairs of integer numbers and sends its output to stdout
mult       reads pairs of numbers from stdin and prints lines with their products
add        reads pairs of numbers from stdin and prints lines with their sums

gennumbers will simply print out the number pairs
gennumbers >numbers.txt  will output the number pairs to the file numbers.txt

mult will simply read in pairs of numbers from the keyboard
mult <numbers.txt will input numbers from the file numbers.txt

gennumbers | mult will pipe stdout of gennumbers to stdin of mult

gennumbers | mult >timestables.txt will send mult's stdout to the file timestables.txt

add is similar to mult but adds the number pairs

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filenumbers generates number pairs and sends its output to the file specified on its command line. For example:

filenumbers numbers.txt

filemult reads number pairs from the file specified on its command line. For example:

filemult numbers.txt

fileadd is similar to filemult but adds the number pairs