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changing a parameter's value within a function
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):
   • Passing information into functions in C - by name, by value - [link]

Source code: astamp.c Module: C204
/* If you pass a variable into a function in C, you copy the contents into the function
so thst any changes made internally in the function are not reflected in the main code copy.
However, if you pass in the address of the variable and work at the same address inside and
outside the function, any changes you make to the variable's contents within the function will
be reflected in the calling code too. */

/* changing a parameter's value within a function */

#include <stdio.h>

void increase(int number) { // "number" is local copy
        printf("Number is %d\n",number);
void boost(int *number) { // "number" is in effect an alias
        printf("Number is %d\n",*number);

int main() {

        int *wherepeople;
        int people;

        printf("How many people yagot? ");
        printf("People is %d\n",people);

        printf("People is %d\n",people);

        printf("People is %d\n",people);

        wherepeople = &people;
        printf("People is %d\n",people);


/* Sample output

WomanWithCat:harwell grahamellis$ ./astamp
How many people yagot? 5
People is 5
Number is 6
People is 5
Number is 6
People is 6
Number is 7
People is 7
WomanWithCat:harwell 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

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
You can learn more about this example on the training courses listed on this page, on which you'll be given a full set of training notes.

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