C writing into pointer array? - c

Question

I have a homework that wants us to make an array of (x,y) coordinates that the user enters but we don't know how many will be entered, it will end when (0,0) is entered, the last one will not be added to the array and then we sort them and print them.So I used pointers to make array but I can't insert all the elements that I want to insert it only recognizes the last entered one. When I try to print them it will print only the last one I entered correctly the others mostly comes (0,0) or some random numbers.
int main()
{
int x,y,*xp,*yp;
int a = 0,s,m=12;
etiket:
scanf("%d %d",&x,&y);
printf("\n");
while (x != 0 || y != 0)
{
a=a+1;
xp = (int*) malloc(sizeof(int)*m);
yp = (int*) malloc(sizeof(int)*m);
//printf("%d %d\n",x,y);
if( a%10==0)
{
xp = (int*) realloc(xp,sizeof(int)*m+10);
yp = (int*) realloc(yp,sizeof(int)*m+10);
}
xp[a]=x;
yp[a]=y;
printf("%d %d\n",*(xp+a),*(yp+a));
goto etiket;
//SortPoints((xp+a),(yp+a),a);
}
//printf("siralama:\n");
//for(s=0; s<=a; s++)
//{
// printf("%d %d\n",*(xp+s),*(yp+s));
//}
}
So this is my work-in-progress code.
I don't even know if it's possible I would appreciate any help.
Thank you in advance.

Answer 1

As you have been restricted to use C it's lot easier to use structure for dynamically allocated memory for arrays. Here's the code:-
#include<stdio.h>
#include<malloc.h>
#define SIZE 20 // SIZE OF YOUR ARRAY FOR DYNAMIC MEMORY ALLOCATION
typedef struct {
int x;
int y; // That's the point with x and y coordinate
} point ; // Similar as int n, float a .... now point is a
// type which holds the value of x and y
int main(void){
point *p; // pointer decleration for point type
p= (point *)malloc(SIZE* sizeof(point)); // Memory Allocation
int i=0;
do{
p++; // increment of pointer
i++;
printf("Enter values for point %d: (x,y)= ",i);
scanf("%d", &p->x); // input x and y
scanf("%d", &p->y);
}while((p->x) !=0 || (p->y) !=0 ); // loop breaks when inputs 0,0
p--; // decrement pointer as 0,0 value will have no use
i--;
printf("\n\n\n");
for(;i>0;i--,p--)
printf("Point %d: (x,y)=(%d,%d)\n", i,p->x, p->y);
// displaying point values user given
printf("\n\n\n");
return 0;
}
Here p holds the hole array of points. Now, for sorting you just have to pass p in a function as a agrument like that and write the regular sorting algorithm inside the body.
point* SortingArray(point *p)
This function will return another arrays of points which is sorted. Hope you could do this yourself.
Furthermore, probably very soon You will learn C++ where this kind of works are so easy using class. In fact, in C++ there have a lot of features in the STL(Standard Template Library) like lists,vectors... for these kind of works which support dynamic memory allocation very soundly.
Let me know if You find any problem to grasp the concept. Thanks.