errror :   implicitly declaring function 'malloc' with type void *(unsigned long )

1. Be sure to include the correct header file.

   #include <stdlib.h>
   
   

2. Casting the return is allowed but frowned upon in C as being unnecessary.

   double* sequence = malloc(...);
   
   

3. Consider the follow style as its easier to maintain and IMO, less error prone.

   double* sequence = malloc(numInSeq * sizeof(* sequence));
   
   

4. Remember the argument type is size_t may differ in size than int.  size_t is the unsigned integer type of the result of the sizeof operator.

   void *malloc(size_t size);
   
   

5. Check the result.

   if (sequence == NULL) Handle_OutOfMemory();
   
   

6. Eventually, free the pointer. It is OK to free the pointer even if it has a NULL value.

   free(sequence);
   
   

7. If there is a chance sequence will get used agian, best to promptly set its value to NULL.

   free(sequence);
   
   sequence = NULL;