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+// FILE: useful.h
+// PROVIDES: A toolkit of useful functions for random numbers and displays.
+//
+// FUNCTIONS in the toolkit:
+//   double random_fraction( )
+//     Postcondition: The return value is a random real number in the closed
+//     interval [0..1] (including the endpoints).
+//
+//   double random_real(double low, double high)
+//     Precondition: low <= high.
+//     Postcondition: The return value is a random real number in the closed
+//     interval [low..high] (including the endpoints).
+//
+//   void display(double x)
+//     Postcondition: The function has written one line of output to the
+//     standard ouput, with a vertical bar in the middle. If x is positive,
+//     then approximately x stars are printed to the right of the vertical
+//     bar. If x is negative, then approximately -x stars are printed to the
+//     left of the vertical bar. If the absolute value of x is more than
+//     39, then only 39 stars are printed.
+//     Examples:
+//     display(8) prints:                          |********
+//     display(-4) prints:                     ****|
+//
+//   void eat_line( )
+//     Postcondition: Up to next newline has been read and discarded from cin.
+//
+//   bool inquire(const char query[ ])
+//     Precondition: query is a null-terminated string of characters.
+//     Postcondition: query has been printed, and a one-line response read 
+//     from the user. The function returns true if the user's response begins 
+//     with 'Y' or 'y', and returns false if the user's response begins with 
+//     'N' or 'n'. (If the response begins with some other letter, then the
+//     query is repeated.)
+
+#ifndef USEFUL_H  // Prevent duplicate definition
+#define USEFUL_H
+
+    double random_fraction( );
+    double random_real(double low, double high);
+    void display(double x);
+    void eat_line( );
+    bool inquire(const char query[ ]);
+
+#endif