说明：  Graph with no options takes pairs of points (two numbers per line) from the given file (or standard input) as x- and y- values and plots them on the screen, connected by straight lines. A string surrounded by quotes "..." may follow a pair of points, and will be displayed starting at that point. If an input file is specified, the program waits for a keypress, then resets the screen parameters and clears the screen before exiting. If the data comes from the standard input, the program exits without clearing the screen or resetting it
(Graph with no options takes pairs of points (two numbers per line) from the given file (or st andard input) as x-and y-values and plots them o n the screen. connected by straight lines. A string surround ed by quotes "..." may follow a pair of points. and will be displayed starting at that point. If an input file is specified, the program waits for a keypress. then resets the screen parameters and clears th e screen before exiting. If the data comes from t he standard input, the program exits without clearing the screen o r resetting it)