foreach.c

#include <stdio.h>

#define length(arr) (sizeof(arr)/sizeof(arr[0]))

#define TOKEN_CONCAT_INNER(x, y) x##y
#define TOKEN_CONCAT(x, y) TOKEN_CONCAT_INNER(x, y)

#define LABEL(id) TOKEN_CONCAT(LABEL_##id##_, __LINE__)

#define foreach(type, name, arr) \
for(int i = 0; i < length(arr); ++i) \
for(type *name;;)\
if (1)\
{\
  name = &arr[i];\
  goto LABEL(block);\
  LABEL(done):\
   break;\
}\
else\
  while(1)\
    if(1)\
    {\
      goto LABEL(done);\
    }\
    else\
      LABEL(block):\

typedef struct Point
{
  float x;
  float y;
} Point;

int main(void) {
  int arr[100] = {0};

  Point points[100] = {0};

  foreach(int, curr, arr)
  {
    *curr = i;
  }

  foreach(int, curr, arr)
  {
    printf("%d\n", *curr);
  }

  foreach(Point, p, points)
  {
    p->x = i;
    p->y = i+1;
  }

  foreach(Point, p, points)
  {
    printf("%f, %f\n", p->x, p->y);
  }

  return 0;
}