storing data using array, pointer and struct in C problem

Question

I have been trying to solve this problem last few days but I still can't figure out... as a newbie learner.

I understand that I suppose to use array, pointer or struct and I tried to apply to it but failed...

Apologise for some Korean language in the code.

What I am trying to do is store each of student information in order to sort and print at the end (see the photo below) result suppose to look like this

What I couldn't figure out is storing the data and printing all students data at the end (3 students) Data I try to store is (name, fullyear, month, day, leapyear, nationality, gender, major) with this order I tried using pointer, array but couldn't do it well.

Any advice would be appreciated and thanks in advance. Please understand English is not my first language and I am a newbie for programming so if my decription isn't enough, I will try to add more later on so feel free to comment. Thank you!

Here is my code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main(void)
{
    int i;
    for (i = 0; i < 3; i++)
    {
        char name[20];
        char major[50];
        char ssn[20];

        printf("%s", "이름 : ");
        scanf("%[^\n]%*c", name);
        //fgets(name, 20, stdin);
        printf("%s", "학과 : ");
        scanf("%[^\n]%*c", major);
        //fgets(major, 50, stdin);
        printf("%s", "주민등록번호 : ");
        //fgets(ssn, 20, stdin);
        scanf("%[^\n]%*c", ssn);

        // last 2 digits of birth year
        char year[3];
        memcpy(year, &ssn[0], 2);
        year[2] = '\0';

        // 2 digits of birth month
        char month[3];
        memcpy(month, &ssn[2], 2);
        month[2] = '\0';

        // 2 digits of birth day
        char day[3];
        memcpy(day, &ssn[4], 2);
        day[2] = '\0';

        // distinguising birth years of 1900
        char fullyear[5];
        if ((ssn[6] == '1') || (ssn[6] == '2') || (ssn[6] == '5') || (ssn[6] == '6'))
        {
            fullyear[0] = '1';
            fullyear[1] = '9';
            fullyear[2] = year[0];
            fullyear[3] = year[1];
            fullyear[4] = '\0';
        }

        // distinguishing birth years of 2000
        if ((ssn[6] == '3') || (ssn[6] == '4') || (ssn[6] == '7') || (ssn[6] == '8'))
        {
            fullyear[0] = '2';
            fullyear[1] = '0';
            fullyear[2] = year[0];
            fullyear[3] = year[1];
            fullyear[4] = '\0';
        }

        // distinguishing birth years of 1800
        if ((ssn[6] == '9') || (ssn[6] == '0'))
        {
            fullyear[0] = '1';
            fullyear[1] = '8';
            fullyear[2] = year[0];
            fullyear[3] = year[1];
            fullyear[4] = '\0';
        }

        // print name
        printf("%s, ", name);
        // print birth year
        printf("%s년 ", fullyear);
        // print month
        printf("%s월 ", month);
        // print day
        printf("%s일, ", day);

        // leap year, converting from full year string --> int
        int leapyear;
        leapyear = atoi(fullyear);
        if (((leapyear % 4 == 0) && (leapyear % 100 != 0)) || (leapyear % 400 == 0))
        {
            printf("윤년, ");
        }
        else
        {
            printf("윤년아님, ");
        }

        // foreigner or Korean
        if ((ssn[6] == '5') || (ssn[6] == '6') || (ssn[6] == '7') || (ssn[6] == '8'))
        printf("외국, ");
        else printf("대한민국, ");

        // gender
        if ((ssn[6] == '1') || (ssn[6] == '3') || (ssn[6] == '5') || (ssn[6] == '7') || (ssn[6] == '9'))
        printf("남자, ");
        else printf("여자, ");

        // print major
        printf("%s\n\n", major);
    }
    return 0;
}

Answer 1

As you have said, you need to use structs. For example, if you'd like to store 3 people (name, surname, and age) you need to do something like this:

typedef struct {
  char name[20];
  char surname[20];
  int age;
} People;

int main() {
  People people[3];
  int x;

  for (x = 0; x < 3; x++) {
    scanf("%[^\n]%*c", people[x].name);
    scanf("%[^\n]%*c", people[x].surname);
    scanf("%d%*c", &people[x].age);
  }

  return 0;
}

Also, take in mind that if the user puts more than 19 characters on the name/surname, will result in overflow. fgets() plus some kind of contol will be better (or other functions), but I suppose it's just an excercice.

An example:

char txt[20];
char next;

scanf("%19[^\n]%c", txt, &next);
if (next == '\n') {
  printf("[*] %s\n", txt);
}
else {
  printf("[e] Error, >19 characters\n");
}

Answer 2

The easiest, most direct way to do what you want is with an (large enough) array of structures

#include <stdio.h>

struct Student {
    char name[200]; // maximum name of each student is 199
    int year, month, day;
    char nationality[100]; // max 99
    char gender[2];
    char major[100]; // max 99
};

int byage(const void *aa, const void *bb) {
    const struct Student *a = aa;
    const struct Student *b = bb;
    if (a->year != b->year) return b->year - a->year;
    if (a->month != b->month) return b->month - a->month;
    return b->day - a->day;
}

int main(void) {
    struct Student data[500]; // maximum 500 students
    int n = data_fill(data); // fill data with user input
    qsort(data, n, sizeof *data, byage); // sort data
    data_print(data, n); // print it
    return 0;
}