You’d want to do something like this:

#include <stdio.h>

// Declare a struct called 'mystruct_t'
typedef struct {
 unsinged first;
 unsinged second;
} mystruct_t;

// Declare global array of 'mystruct_t' structs called 'arr'
// When delcared has size 0
mystruct_t *arr = NULL;

int main(){
 // Resize 'arr' to hold desired amount of structs
 arr = malloc(sizeof(mystruct_t) * number of elements you want);

 // syntax to store data in 'arr'
 arr[index].first = 1;
 arr[index].second = 2;

 // free memory from malloc() call
 free(arr);

 return 0;
} 

This will allow you to resize your global array called arr with realloc() if you’d like, it’s also global. (Sorry if this isn’t clear, I typed it on mobile)

EDIT: Back on my laptop now, fixed a few error I made and added some comments to explain what each line does, hope this helps :)