Symbolic Constants

The numbers 0, 20, and 300 in the program mean very little to readers of the program unless they are very familiar with what the program is doing

for (fahr=0; fahr <= 300; fahr = fahr+20)

C allows the definition of symbolic constants - names that will be replaced with their values when the program is compiled
Symbolic constants are defined before main(), and the syntax is

Example:

// program name: temp_conv2.c

        #include <stdio.h>

        #define LOWER   0   /* lower limit of table */

        #define UPPER   300 /* upper limit */

        #define STEP    20  /* step size */

        main()

               int fahr;

               for (fahr=LOWER; fahr<=UPPER; fahr=fahr+STEP)

               {
                       printf("%3d %6.1f\n",fahr,(5.0/9.0)*(fahr-32));

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