Class notes from 2/5

advanced.c

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

struct _book {
	int bookid : 3;
};
typedef struct _book book;


union _magazine {
	int id;
	float value;
	char title[20];
};
typedef union _magazine magazine;

int intcmp(const void *x, const void *y){

	return -(*(int*) x - *(int*)y);
}

int main(int argc, char *argv[]) {

	printf("Book size: %ld\n", sizeof(book));
	book textbook;
	textbook.bookid = 8; // 1000
	printf("Textbook.id: %d\n", textbook.bookid);
	textbook.bookid = 2; // 10
	printf("Textbook.id: %d\n", textbook.bookid);
	textbook.bookid = 7; // 111
	printf("Textbook.id: %d\n", textbook.bookid);
	textbook.bookid = 7; // 111
	printf("Textbook.id: %ud\n", (unsigned) textbook.bookid);

	// --------------
	/*
	 * 0x 01234567
	 * Big endian
	 * [01] 0x100
	 * [23] 0x101
	 * [45] 0x102
	 * [67] 0x013
	 *
	 * Little endian
	 * [67] 0x100
	 * [45] 0x101
	 * [23] 0x102
	 * [01] 0x013
	 *
	 */

	// ---------------
	//
	printf("Union size: %ld\n", sizeof(magazine));
	magazine time;

	time.id = 1234;
	printf("id: %d, value: %f, title: '%s'\n", time.id, time.value, time.title);

	time.value = 19.99;
	printf("id: %d, value: %f, title: '%s'\n", time.id, time.value, time.title);

	strcpy(time.title, "Person of the year");
	printf("id: %d, value: %f, title: '%s'\n", time.id, time.value, time.title);

	printf("%p, %p \n", &time.id, &time.value);


	//------------------------------
	int array[] = {10,23,256,5,32};

	qsort(array, 5, sizeof(int), intcmp);
	for(int i =0; i < 5; ++i) {
		printf("=> %d\n", array[i]);
	}

	return 0;
}

structure.c

// Class activity solution

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

struct _course
{
    int student_id;
    int marks;
    char subject[20];   
    //char *subject;   
};
typedef struct _course course;

int main()
{
    // Task1: Create a pointer variable ptr for the structure course
    course * ptr;

    int i, no_of_records;
    printf("Enter number of records: ");
    scanf("%d", &no_of_records);

    // TODID Task 2: Allocate the memory for no_of_records structures with pointer ptr pointing to the base address.
    ptr = calloc(no_of_records, sizeof(course)); 

    // Iterate through the no_of_records to get information from the user for each record
    for(i = 0; i < no_of_records; ++i) {
        printf("Enter the student id,name of the subject and marks respectively:\n");
        
        //TODID Task 3: Get the info id, name of the subject followed by the student mark
	/*course tempcourse;
	scanf("%d %s %d", &tempcourse.student_id, tempcourse.subject, &tempcourse.marks );
	ptr[i].student_id = tempcourse.student_id;
	ptr[i].marks = tempcourse.marks;
	strcpy(ptr[i].subject, tempcourse.subject);*/
	//scanf("%d %s %d", &ptr[i].student_id, ptr[i].subject, &ptr[i].marks );
	course tempcourse;
	scanf("%d %s %d", &tempcourse.student_id, tempcourse.subject, &tempcourse.marks );
	// ptr[i] = tempcourse; // changing what ptr[] is pointing to BAD
	memcpy(&ptr[i], &tempcourse, sizeof(course)); // Copy into the allocated memory
    }

    // If stuff happened here we would get strange errors

    printf("Displaying Student Information:\n");
    for(i = 0; i < no_of_records ; ++i) {
        printf("Student ID: %d\n",(ptr+i)->student_id);
        printf("%s\t%d\n", (ptr+i)->subject, (ptr+i)->marks);
    }
    free(ptr);
    return 0;
}