How to resolve “parameter has incomplete type” error?

Question

I\'m a newbie and I need help with debugging my code. When I compile it \'type of formal parameter 1 is incomplete\' and type of formal parameter 2 is incomplete\' error appears

Answer 1

Your program is showing incomplete type error because the scope of struct date is limited to main() function only. Outside the main() the structure definition is not visible.

So, the struct date definition should be in global scope so that it is visible from calc_age() (and maybe other functions, too). Even better, if you can create and maintain a header file for this purpose.

That said, in your code, as per your current requirement, get rid of single-element arrays in the structure, like

struct date {
    int month;
    int day;
    int year;
 };

and also, the scanf() statement

scanf("%d %c %d %c %d", birth.month, &c, birth.day, &c, birth.year);

should read

scanf("%d %c %d %c %d", &birth.month, &c, &birth.day, &c, &birth.year);

Answer 2

#include <stdio.h>
struct date {
    int month[1];
    int day[1];
    int year[1];

};

int calc_age (struct date birth, struct date current);


int main(void)
{
struct date birth, current;
char c;

printf("Input the birthdate (MM/DD/YY): ");
scanf("%d %c %d %c %d", birth.month, &c, birth.day, &c, birth.year);
printf("Input date to calculate (MM/DD/YY): ");
scanf("%d %c %d %c %d", current.month, &c,  current.day, &c, current.year);

printf("Age is %d years.\n", calc_age(birth, current));

return 0;

}

int calc_age (struct date birth, struct date current) {
int age;

if (birth.month[0] < current.month[0]) {
    age = (current.year[0] - birth.year[0]);
} else if (birth.month[0] > current.month[0]) {
    age = (current.year[0] - birth.year[0] - 1);
} else {
    if (birth.day[0] <= current.day[0]) {
        age = (current.year[0] - birth.year[0]);
    } else {
        age = (current.year[0] - birth.year[0] - 1);
    }
}

return age;
}

You should define the struct before main