I try to pass a variable by reference to a function and change its value. Inside that function it works but when I print the value of the variable outside the function the value is different.. I'd like to understand what I am doing wrong as I need it for my program..

I declare this variable as global plus the definition of two functions outside (before) the main function:

int a;
 
void change_sound_1(int *);
void change_sound_2(int *);
 
.....

inside the main function i have this code:

switch(code)
{
     case 0:
     IDOS->Printf("Sound rate is: 11025\n");
     change_sound_1(&sound_code);
     IDOS->Printf("sound_code is:%d\n", sound_code);
     break;
 
     case 1:
     IDOS->Printf("Sound rate is: 22050\n");
     change_sound_2(&sound_code);
     IDOS->Printf("sound_code is:%d\n", sound_code);
     break;
}
 
break;

These are the two functions that I use to modify the int variable:

void change_sound_1(int *a){
	*a=0;
	printf("sound code is:%d\n", *a);
 	*a=*a+1;
	printf("sound code is:%d\n", *a);
}
 
void change_sound_2(int *b){
	*b=0;
	printf("sound code is:%d\n", *b);
	*b=*b+2;
	printf("sound code is:%d\n", *b);
}

But when i print the variable, for the second time, in the main function, it prints 0 (zero).. Shouldn't it print the the same value that the two functions print? as I have modified its value using the pointer??