Thread: Main with Merge Sort Function - Help Please

Hi, could someone please help me with my main function that has merge sort in it?
I'm not sure how to call it or how this should be set up. I read in a file that has students and they are supposed to be sorted by their birthday, like JANUARY 5, and we find who has the closest birthday to someone else. The file reads in first name, last name, month, day, and year on the same line, but year is not used in the sorting. The queried students are part of the class, and I'm supposed to find the name of the student not queried with the closest birthday to the queried student.

This is what I have for main:

Code:

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

#define MAXLENGTH 30

struct student {
	char first_name[MAXLENGTH];
	char last_name[MAXLENGTH];
	int month[12];
	int day;
	int year; //not used for sorting the birthdays
};

int Is_Sorted(struct student *val[], int length);
void MergeSort(struct student *val[], int low, int high);
void Merge(struct student *val[], int low, int middle, int high);
void Print_Array(struct student *val[], int length);

int main ()
{
	int num_classes;
	int month[12] = {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 394, 334};
	FILE* ifp;
	ifp = fopen("birthday.txt", "r");
	
	struct student *info;
	info = (struct student*)(malloc(sizeof(struct student)*MAXLENGTH));
	
    fscanf(ifp, "%d ", &num_classes);
    
    int i, j;
    
    // Loop through each class
    for (i=1; i<=num_classes; i++) 
	{
		//Beginning Output
        printf("Class #%d:\n\n", i);
        
        int num_students;
        fscanf(ifp, "%d", &num_students);
         
        for(j=0; j<num_students; j++)
        {
            
            char first_name[MAXLENGTH];
            char last_name[MAXLENGTH];
            char month[MAXLENGTH];
            
            int day, year;
            fscanf(ifp, "%s ", first_name);
            fscanf(ifp, "%s ", last_name);
            fscanf(ifp, "%s ", month);
            fscanf(ifp, "%d ", &day);
            fscanf(ifp, "%d ", &year);
        }
        
        int num_queries;
        char queried_firstname[MAXLENGTH];
        char queried_lastname[MAXLENGTH];
        
        fscanf(ifp, "%d", &num_queries);
        
        for(j=0; j<num_queries; j++)
        {
            fscanf(ifp, "%s ", queried_firstname);
            fscanf(ifp, "%s ", queried_lastname);
        }
	}
	
	// Sort the Values
    MergeSort(&info, 0, MAXLENGTH-1);
    	//Print_Array(val, SIZE);

    // Check if it's sorted.
    if (Is_Sorted(&info, MAXLENGTH))
        //printf("Sorted correctly.\n");
        
    /*
	int dayofyear;
    for(i=0; i<12; i++)
	{
		dayofyear = month[i] + day;
   		differenceleft = month[i] - month[i-1];
   		differenceright = month[i+1] - month[i];

   		if (differenceleft < differenceright)
   			//middle person closest to person on left
   			printf("%s %s has closest birthday to %s %s", first_name, last_name, 
                        queried_firstname, queried_lastname);
   		else if(differenceright < differenceleft)
      	//middle person closest to person on right
	}
	*/
	
	free(info);
	fclose(ifp);
	system ("PAUSE");
	return 0;
}

Your saying the &info part of the Mergesort is wrong right? I already have this

struct student *info;
info = (struct student*)(malloc(sizeof(struct student)*MAXLENGTH));

Are you saying I should make another array that's not part of the struct?

First thing to fix is this:

You need to #include <stdlib.h> so you can use malloc().

Further down, it looks like you've read in all the students data from the file, but then you somehow begin reading the queried students data, from the file??

Code:

         
        for(j=0; j<num_students; j++)
        {
            
            char first_name[MAXLENGTH];
            char last_name[MAXLENGTH];
            char month[MAXLENGTH];
            
            int day, year;
            fscanf(ifp, "%s ", first_name);
            fscanf(ifp, "%s ", last_name);
            fscanf(ifp, "%s ", month);
            fscanf(ifp, "%d ", &day);
            fscanf(ifp, "%d ", &year);
        }
        
        int num_queries;
        char queried_firstname[MAXLENGTH];
        char queried_lastname[MAXLENGTH];
        
        fscanf(ifp, "%d", &num_queries);
        
        for(j=0; j<num_queries; j++)
        {
            fscanf(ifp, "%s ", queried_firstname);
            fscanf(ifp, "%s ", queried_lastname);
        }
	}

Maybe you meant the part in blue to use scanf() instead or is there still num_queries students data to be read in the data file?

And you'll want to use a for loop probably, to make your array of pointers point to each struct, after you malloc the pointer array very similarly to how you malloc'd the array of structs, except you add the extra * so each pointer is just the size of a struct pointer, and not the size of a struct.

And if you even THINK about using Soul's mergesort algorithm, we'll have to ship you off to the North Pole, never to be heard from again!

Code:

        struct student *info;
	info = (struct student*)(malloc(sizeof(struct student)*MAXLENGTH));
	
	for (i=0; i<MAXLENGTH-1; i++)
	{
		int *value[i];
    	        value[i] = (int*)(malloc(sizeof(int)*MAXLENGTH));
	}

Did you mean using two *? Do I set value[i] equal to struct student *info?

Originally Posted by Hikaru90

Code:

        struct student *info;
	info = (struct student*)(malloc(sizeof(struct student)*MAXLENGTH));
	
	for (i=0; i<MAXLENGTH-1; i++)
	{
		int *value[i];
    	        value[i] = (int*)(malloc(sizeof(int)*MAXLENGTH));
	}

Did you mean using two *? Do I set value[i] equal to struct student *info?

I thought info was your array of structs, (almost), and value was going to be your array of pointers to the structs.

So every element of value would need a malloc(sizeof( struct student *) * MAXLENGTH).
One * next to student, inside the ), and one for multiplication just outside the ).

Or did you have something else in mind?

Trust me, when you get to ** pointers and especially *** pointers, my head starts complaining!

Hey dude, did you see my topic on this board? You and I have the exact same assignment. Is it possible we have the same teacher/class/university? lol

Code:

        struct student *info;
	info = (struct student*)(malloc(sizeof(struct student)*MAXLENGTH));
	
	for (i=0; i<MAXLENGTH-1; i++)
	{
		int *value[i];
    	        value[i] = (struct student*)(malloc(sizeof(struct student)*MAXLENGTH));
	}

Does it matter if I have it this way instead of malloc(sizeof(struct student*)*MAXLENGTH)?

@ Soul, lol I don't know, maybe.

ok so

Code:

struct student *info;
info = malloc(sizeof(struct student)*MAXLENGTH));
	
for (i=0; i<MAXLENGTH-1; i++)
{
     int *value[i];
     value[i] = malloc(sizeof(struct student*)*MAXLENGTH);
}

yeah I don't think that's what I'm supposed to do, and I didn't realize that it mattered that I do the dayofyear now. I created a function for the day of year, so like if month = January, dayofyear = day. So February 4 would be the 35th day of the year.
For example:

Code:

void CalculateDayofYear(struct student *info[])
{
    for(i=0; i<num_students; i++)
    {
        if(strcmp(info[i]->month, "JANUARY")==1)
            info[i].dayofyear == info[i]->day;
        else if ...
    }
}

Then I guess the people would be sorted according to their dayofyear, so I'm not really sure how to put that into mergesort or make sure mergesort sorts that.

@ Soul - Well, I don't really wanna give out my info.