The main program keeps track of information on members of a health club. It calls a function AddMember() when there is a new membership. The membership counts are kept track of in main(), so main() could pass this info to other functions.
void main()
{
int total_cnt, At memory location 1000
family_cnt, At memory location 2000
adult_cnt, At memory location 1600
child_cnt; At memory location 2200
The variables above are known to main(), not AddMember(). AddMember() will not recognize their names.
The function header for AddMember is
void AddMember(int *totalptr, int *fptr, int *aptr, int *cptr)
where totalptr is a pointer to the total count (total_cnt), fptr is a pointer to the family count (family_cnt), etc.
1. Write a calling statement for AddMember(), from
main.
AddMember(&total_cnt, &family_cnt, &adult_cnt,
&child_cnt);
2. Assume the variables have these current values, total_cnt = 204, family_cnt = 52, adult_cnt = 108, child_cnt = 96, when main() calls AddMember(). In the chart below, write the value of the expression, or check the ERROR column if the expression would result in a syntax error.
VALUE ERROR If the expresion is IN main total_cnt 204 _____ &total_cnt 1000 _____ *totalptr __________ __X__ &totalptr __________ __X__ Main does not recognize totalptr. adult_cnt 108 _____ &adult_cnt 1600 _____ &child_cnt 2200 _____ *family_cnt __________ __X__ Variable family_cnt is not a pointer, so you can not dereference it.
If the expression is IN AddMember totalptr 1000 _____ fptr 2000 _____ *aptr 108 _____ &cptr *** _____ &total_cnt __________ __X__ *total_cnt __________ __X__ AddMember does not know what total_cnt is. *totalptr 204 _____ *fptr 52 _____
*** Since cptr is a variable, its value is stored somewhere, so IT DOES have an address, you just don't know what it is. Just using &cptr will not get an error, because THERE IS an address, but it probably is not what you intended. Writing something like &cptr = 20 WILL get an error.
NOTE: &total_cnt = 1000 = totalptr. So we usually have &variablename in the calling statement when the argument is a pointer data type. (NOT *variablename, even though the * is in the function header!!)
adult_cnt = 108 = *aptr. So we usually use *pointername in the code of the function when the argument is a pointer data type.