Training, Open Source Programming Languages

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call by value v call by pointer / reference
Functions, Macros and programs in multiple files example from a Well House Consultants training course
More on Functions, Macros and programs in multiple files [link]

This example is described in the following article(s):
   • Some new C programming examples - files, structs, unions etc - [link]

Source code: fundy.c Module: C204

/* Variable declared OUTSIDE the functions
is shared between all the functions! */

int ticker = 0;

/* Use of call by value to double copies contents
of variable in to function, and means that any
changes made to incoming data are NOT reflected in
calling code.

Call by pointer (or reference or name) to triple
means that changes to the contents of that variable
made within the function ARE reflected in the
calling code
*/


float dubble (float what) {
        /* result and what are LOCAL to dubble */
        float result;
        result = what * 2.0;
        ticker++;
        return result;
        }
float triple (float *wherestuff) {
        *wherestuff *= 3.0;
        return 1;
        }
int main () {
        /* res is local to main */
        float res;
        float stuff;
        float boat = 16.0;
        /* demo does NOT contain a float ...
        ... it contains a POINTER to a float! */

        float *demo;
        ticker++;
        res = dubble(5.0);
        demo = &stuff;
        stuff = 8.0;
        triple(demo);
        triple(&stuff);
        printf ("Result is %f\n",res);
        printf ("Ticker is %d\n",ticker);
        printf ("Stuff is %f\n",stuff);
        printf ("demo is %x\n",demo);
        demo++;
        printf ("demo is %x\n",demo);
        printf ("demo points to %f\n",*demo);
        }

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

Books covering this topic
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Other Examples
This example comes from our "Functions, Macros and programs in multiple files" training module. You'll find a description of the topic and some other closely related examples on the "Functions, Macros and programs in multiple files" module index page.

Full description of the source code
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