C-Kurs/Studentendatenbank/Musterlösung

Musterlösung

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

#define ANZAHL 10
#define NAME_LEN 25

#define NAME_TO_LONG (-1)
#define MAT_NR_USED (-2)
#define DB_FULL (-3)
#define ADD_SUCCEED 1
#define NO_MAT_NR (-1)
#define DEL_SUCCEED 1

/* Teil a */
typedef struct student_t {
	int mat_nr;
	char first_name[NAME_LEN];
	char last_name[NAME_LEN];
} student;

/* Teil b */
void print_student(student *studi) {
	printf("Matr.Nr.: %i, Vorname: %s, Nachname: %s\n", studi->mat_nr, studi->first_name, studi->last_name);
}

/* Teil c */
void print_students_db(student **db) {
	printf("===========================================================\n");
	int i;
	for (i=0; i<ANZAHL; i++) {
		if (db[i] != NULL) {
			print_student(db[i]);
		}
	}
	printf("===========================================================\n");
}

/* Teil e */
void clear_db(student **db) {
	int i;
	for (i=0; i<ANZAHL; i++) {
		if (db[i] != NULL) {
			free(db[i]);
			db[i] = NULL;
		}
	}
}

/* Teil f */
int get_student_index(int mat_nr, student **db) {
	int i;
	for (i=0; i<ANZAHL; i++) {
		if (db[i] != NULL) {
			if (mat_nr == db[i]->mat_nr) {
				return i;
			}
		}
	}
	return -1;
}

int add_student(int mat_nr, char *first_name, char *last_name, student **db) {
	if (strlen(first_name) >= NAME_LEN || strlen(last_name) >= NAME_LEN) {
		return NAME_TO_LONG;
	}
	if (get_student_index(mat_nr, db) >= 0) {
		return MAT_NR_USED;
	}

	int i;
	for (i=0; i<=ANZAHL; i++) {
		if (db[i] == NULL) {
			db[i] = malloc(sizeof(student));
			db[i]->mat_nr = mat_nr;
			strcpy(db[i]->first_name, first_name);
			strcpy(db[i]->last_name, last_name);
			return ADD_SUCCEED;
		}
	}
	return DB_FULL;
}

/* Teil g */
int del_student(int mat_nr, student **db) {
	int del_student_index = get_student_index(mat_nr, db);
	if (del_student_index < 0) {
		return NO_MAT_NR;
	}
	free(db[del_student_index]);
	db[del_student_index] = NULL;
	return DEL_SUCCEED;
}

int main() {
	/* Teil b*/ printf(">>> Teil b\n");
	student *one_student = malloc(sizeof(student));
	one_student->mat_nr = 123456;
	strcpy(one_student->first_name, "Max");
	strcpy(one_student->last_name, "Mustermann");
	print_student(one_student);

	/* Teil c */ printf(">>> Teil c\n");
	student *all_students[ANZAHL];
	int i;
	for (i=0; i<ANZAHL; i++) {
		all_students[i] = NULL;
	}
	all_students[0] = one_student;
	print_students_db(all_students);

	/* Teil d */ printf(">>> Teil d\n");
	all_students[1] = malloc(sizeof(student));
	all_students[1]->mat_nr=653321;
	strcpy(all_students[1]->first_name, "Herbert");
	strcpy(all_students[1]->last_name, "Meier");
	all_students[2] = malloc(sizeof(student));
	all_students[2]->mat_nr=765431;
	strcpy(all_students[2]->first_name, "Hubertine");
	strcpy(all_students[2]->last_name, "Schulze");
	free(all_students[0]);
	all_students[0] = NULL;
	print_students_db(all_students);

	/* Teil e */ printf(">>> Teil e\n");
	clear_db(all_students);

	/* Teil f */ printf(">>> Teil f\n");
	if (add_student(123456, "Peter", "Mueller", all_students) == ADD_SUCCEED) {
		printf("Student hinzugefuegt.\n");
	}
	if (add_student(123456, "Hans", "Wurst", all_students) == MAT_NR_USED) {
		printf("Student nicht hinzugefuegt, da Mat.nr. schon benutzt wird.\n");
	}
	if (add_student(123457, "Hans", "Wurst", all_students) == ADD_SUCCEED) {
		printf("Student hinzugefuegt..\n");
	}
	print_students_db(all_students);

	/* Teil g */ printf(">>> Teil g\n");
	if (del_student(123456, all_students) == DEL_SUCCEED) {
		printf("Student entfernt.\n");
	}
	print_students_db(all_students);
}

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