When a C program calls a function, the arguments of that function are copied from the calling function to the function definition by default. This method of passing arguments from calling function to the function definition is called Pass-by-Value. Any change that you make to the arguments inside the function will not change the argument's value in the calling function. This is demonstrated in the example below
#include <stdio.h>
void count_update(int, int);
void count_update(int i, int j)
{
i = i + 1;
j = j + 2;
printf("The value of i inside count_update function is %d \n", i);
printf("The value of j inside count_update function is %d \n", j);
return;
}
main()
{
int i, j;
i = 10;
j = 15;
count_update(i, j);
printf("The value of i inside main function is %d \n", i);
printf("The value of j inside main function is %d \n", j);
return 0;
}The output of this program is
The value of i inside count_update function is 11 The value of j inside count_update function is 17 The value of i inside main function is 10 The value of j inside main function is 15
In the above example the value of variables i and j are modified by the count_update() function but their original values inside the main() function remains unchanged.
Another method of passing arguments to a function in C is called Pass by Reference. In this method you pass pointers as arguments to a function. Any modifications the function makes on the pointer's value will also be reflected on the calling function. Pass by Reference is explained in detail in the Pointers in Functions chapter of this tutorial.
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