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Preprocessor directive demonstration
Standard Libraries and other headers example from a Well House Consultants training course
More on Standard Libraries and other headers [link]

This example is described in the following article(s):
   • C and C++ - preprocess, compile, load, run - what each step is for - [link]

Source code: ten.c Module: C211
#include <stdio.h>

/* Demonstration that shows a number of preprocessor directives; the preprocessor is
run prior to the main compile stage and alters the source code prior to its conversion
to a binary / machine level format */

/* Define some preprocessor constants */

#define START 10
#define END 230

/* Define another preprocessor constant but ONLY if it has not been defined before
hand - such as on the command line */

#ifndef STEP
#define STEP 10

main () {

        int current;
        float degc;

/* The preprocessor constants are used in the following statement - by substituting a
constant values prior to coversion to a binary format, the resultant executable progam
can have the efficienciy of being compiled with unchanging (constant) values, and yet
has a degree of flexibility in that it may be recompiled and rebuilt at a later date
with different values */

        for (current = START; current <= END; current += STEP) {
                degc = ((float)current - 32.0) / 9.0 * 5.0;
                printf ("From %3d deg F to %6.2f deg C\n",
                        current, degc);

/* Compile and run samples, showing command line definition of a preprocesor constant

munchkin:capr grahamellis$ gcc -o ten ten.c
munchkin:capr grahamellis$ ./ten
From 10 deg F to -12.22 deg C
From 20 deg F to -6.67 deg C
From 30 deg F to -1.11 deg C
From 40 deg F to 4.44 deg C
From 50 deg F to 10.00 deg C
From 60 deg F to 15.56 deg C
From 70 deg F to 21.11 deg C
From 80 deg F to 26.67 deg C
From 90 deg F to 32.22 deg C
From 100 deg F to 37.78 deg C
From 110 deg F to 43.33 deg C
From 120 deg F to 48.89 deg C
From 130 deg F to 54.44 deg C
From 140 deg F to 60.00 deg C
From 150 deg F to 65.56 deg C
From 160 deg F to 71.11 deg C
From 170 deg F to 76.67 deg C
From 180 deg F to 82.22 deg C
From 190 deg F to 87.78 deg C
From 200 deg F to 93.33 deg C
From 210 deg F to 98.89 deg C
From 220 deg F to 104.44 deg C
From 230 deg F to 110.00 deg C
munchkin:capr grahamellis$ gcc -o ten -DSTEP=17 ten.c
munchkin:capr grahamellis$ ./ten
From 10 deg F to -12.22 deg C
From 27 deg F to -2.78 deg C
From 44 deg F to 6.67 deg C
From 61 deg F to 16.11 deg C
From 78 deg F to 25.56 deg C
From 95 deg F to 35.00 deg C
From 112 deg F to 44.44 deg C
From 129 deg F to 53.89 deg C
From 146 deg F to 63.33 deg C
From 163 deg F to 72.78 deg C
From 180 deg F to 82.22 deg C
From 197 deg F to 91.67 deg C
From 214 deg F to 101.11 deg C
munchkin:capr grahamellis$


Learn about this subject
This module and example are covered on the following public courses:
 * Learning to Program in C
 * Learning to program in C and C++
 * Programming in C
 * C and C++ Programming
 * Learning to program in C and C++
 * C and C++ Programming
Also available on on site courses for larger groups

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Other Examples
This example comes from our "Standard Libraries and other headers" training module. You'll find a description of the topic and some other closely related examples on the "Standard Libraries and other headers" module index page.

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