Sorting a structure - c

Question

I wanted to sort this problem in C with something like bubble sort ... anyone can help
Implement a list with 5 struct Point (Being this a point w/ X, y);
Sort the 5 struct point (first evaluate x then y).
Example:
// The points
p[0]={2,3}
p[1]={4,5}
p[2]={1,5}
p[3]={4,3}
p[4]={1,2}
// Should become
p[0]={1,2}
p[1]={1,5}
p[2]={2,3}
p[3]={4,3}
p[4]={4,5}

Answer 1

If you want to sort structures, you still have to break it down into comparing numeric types. With this in mind, let's take your example with the points:
struct tagPoint
{
int x;
int y;
};
typedef struct tagPoint Point;
Now, let's suppose you have an array of Point and you want it sorted. You can take two approaches:
1. Straightforward function which sorts the array:
Just make the function to sort the array:
void SortPointArray(Point* Points, unsigned int n)
{
/* This will sort the points with priority on the x and then the y value in ascending order. */
for(unsigned int i = 0; i < n-1; i++)
for(unsigned int j = i+1; j < n; j++)
{
if (Points[i].x > Points[j].x)
{
Point aux = Points[i];
Points[i] = Points[j];
Points[j] = aux;
}
else if ((Points[i].x == Points[j].x) && (Points[i].y > Points[j].y))
{
Point aux = Points[i];
Points[i] = Points[j];
Points[j] = aux;
}
}
}
2. Wrap the algorithm in a generic function and use callbacks for each type you want to sort:
This is a little more complicated, but it will save you some time if you use it frequently. Here, this function uses the same algorithm as the one above, but can sort any types.
void Sort(void* lpArray, unsigned int n, size_t cbSize, int (*Cmp)(void*, void*), void (*Swap)(void*, void*))
{
for(unsigned int i = 0; i < n-1; i++)
for(unsigned int j = i+1; j < n; j++)
/* Cast void* to char* to get rid of warning with pointer arithmetic... */
if ( Cmp( ((char*)lpArray) + i*cbSize, ((char*)lpArray) + j*cbSize) )
Swap( ((char*)lpArray) + i*cbSize, ((char*)lpArray) + j*cbSize );
}
As you can see, it requires 2 more functions passed as parameters. If you want this Sort function to know how to sort the Point array, you must define a Comparrison function and a Swapping function and tell the Sort function to use them.
Here is how i implemented them:
/** This function return 1 if p1 should be swapped with p2. */
int ComparePoints(void* vp1, void* vp2)
{
Point *p1, *p2;
p1 = vp1;
p2 = vp2;
if (p1->x > p2->x)
return 1;
else if ((p1->x == p2->x) && (p1->y > p2->y))
return 1;
return 0;
}
/** This will swap 2 points. */
void SwapPoints(void* vp1, void* vp2)
{
Point p = *(Point*)vp1;
*(Point*)vp1 = *(Point*)vp2;
*(Point*)vp2 = p;
}
How do you use them?
If you only want to use the first SortPointArray function, this is enough:
int main()
{
Point Array[10];
/* Read the points. */
for(unsigned int i = 0; i < 10; i++)
scanf("%d %d", &Array[i].x, &Array[i].y);
SortPointArray(Array, 10);
/*Print the points.*/
for(unsigned int i = 0; i < 10; i++)
printf("%d %d\n", Array[i].x, Array[i].y);
return 0;
}
But if you want to use the generic Sort function (which i recommend only if you have multiple types you want to sort like Points, Lines etc) you have to define the two callbacks (ComparePoints and SwapPoints)
int main()
{
Point Array[10];
/* Read the points. */
for(unsigned int i = 0; i < 10; i++)
scanf("%d %d", &Array[i].x, &Array[i].y);
Sort(Array, 10, sizeof(Point), ComparePoints, SwapPoints);
/*Print the points.*/
for(unsigned int i = 0; i < 10; i++)
printf("%d %d\n", Array[i].x, Array[i].y);
return 0;
}

Answer 2

The OP is asking for a C solution, so here you go:
void bsortDesc(struct yourStruct list[80], int s)
{
int i, j;
struct yourStruct temp;
for (i = 0; i < s - 1; i++)
{
for (j = 0; j < (s - 1-i); j++)
{
if (list[j].marks < list[j + 1].marks)
{
temp = list[j];
list[j] = list[j + 1];
list[j + 1] = temp;
}
}
}
}
Also, here's what I got it from: here.