c - skyline algorithm confusion - c

Question

I am trying to write a code which gives coordinates of corners of a skyline, it was one of my friends' homework and I am trying it as a practice for myself. So, here is my code:
#include <stdio.h>
#include <stdlib.h>
typedef struct building
{
int start, height, width;
} BUILDING;
int main()
{
FILE *buildingsptr, *outlineptr;
char karakter;
int satir = 1, i = 0, j = 0, *heights, lastpoint = 0 ;
BUILDING *ptr, *a, temp;
buildingsptr = fopen("buildings.txt", "r");
if (buildingsptr == NULL)
{
printf("An error occured while opening the file.\n");
system("PAUSE");
return 0;
}
while ((karakter = fgetc(buildingsptr)) != EOF)
{
if (karakter == '\n') satir++;
}
ptr = (BUILDING *) malloc(satir * sizeof(BUILDING));
a = ptr;
rewind(buildingsptr);
for (i = 0; i < satir; i++)
{
fscanf(buildingsptr, "%d %d %d", &ptr->start, &ptr->height, &ptr->width);
ptr++;
}
fclose(buildingsptr);
ptr = a; // a is for accessing the first part of the allocated memory,
// compiler gave some errors while I tried to access the first
// block of the array.
for (j = 0; j < satir; j++) //bubble sort to buildings
{
for (i = 0; i < satir; i++)
{
if (ptr[i].start > ptr[i + 1].start)
{
temp = ptr[i];
ptr[i] = ptr[i + 1];
ptr[i + 1] = temp;
}//end of if
}//end of second for
}//end of first for
lastpoint = ((ptr[satir - 1].start + ptr[satir - 1].width) + 1);
heights = (int *)calloc(lastpoint, sizeof(int));
for (j = 0; j < lastpoint; j++) // j travels the x axis
{
for (i = 0; i < satir; i++) // i counts buildings
{
if (j <= (ptr[i].start + ptr[i].width && ptr[i].start <= j))
{
if (ptr[i].height > heights[i])
heights[i] = ptr[i].height;
}
}
}
outlineptr = fopen("outline.txt", "w");
for (i = 0; i < lastpoint; i++) // for every point x,checking the heights
// and transforming them as the coordinates
{
if (heights[i + 1] > heights[i])
{
fprintf(outlineptr, "(%d,%d),", i + 1, heights[i]);
fprintf(outlineptr, "(%d,%d),", i + 1, heights[i + 1]);
}//end if
if (heights[(i + 1)] < heights[i])
{
fprintf(outlineptr, "(%d,%d),", i, heights[i]);
fprintf(outlineptr, "(%d,%d),", i, heights[i + 1]);
}//end if
}//end for
fprintf(outlineptr, "(%d,%d),", lastpoint, heights[lastpoint]);
fprintf(outlineptr, "(%d,%d)", lastpoint, 0);
getch();
return 0;
}
Code is working but it is writing wrong coordinates to the outline.txt. "buildings.txt" is something like:
24 7 4
5 7 11
26 9 7
9 5 5
3 12 4
33 9 6
37 5 7
12 9 10
First integer is starting point of a building, second one is height of the building and third one is width of the building. So, how can I re-write this code? I edited my code to be more proper.

Answer 1

This is a basic example of how the frame of your program should look.
The implementation of the algorithm itself should be up to you.
There is no need for separate line counting.
#include <stdio.h>
#include <stdlib.h>
typedef struct building
{
int start, height, width;
struct building *next;
struct building *prev;
} BUILDING;
int main()
{
FILE *inputFilePtr;
inputFilePtr = fopen("input.txt", "r");
if (inputFilePtr == NULL)
{
printf("An error occured while opening the file.\n");
return EXIT_FAILURE;
}
struct building *build = malloc(sizeof(*build));
struct building *reserve = build;
reserve->prev = NULL;
build->prev = NULL;
char lineBuf[1024];
while (fgets(lineBuf, 1024, inputFilePtr) != NULL)
{
sscanf(lineBuf, "%d %d %d", &(build->start), &(build->height), &(build->width));
build->next = malloc(sizeof(*build));
build->prev = build;
build = build->next;
}
build->next = NULL;
fclose(inputFilePtr);
/////////
// whatever logic comes here
////////
FILE *out = fopen("out.txt","w");
if (out == NULL) return EXIT_FAILURE;
// modify output function to fit your algorithm
while(reserve->next != NULL)
{
fprintf(out, "Build coordinates: (%d, %d, %d)\n", reserve->start, reserve->height, reserve->width);
reserve->prev = reserve;
reserve = reserve->next;
}
fclose(out);
// possible memory cleanup
/*
while(reserve->prev != NULL)
{
reserve = reserve->prev;
free(reserve->next);
}
*/
return 0;
}