struct organism
{
   char fitness;
   int *dna;
};
void main()
{
   struct organism *Agent; //intiialize struct organism to pointer Agent
   Agent.dna = malloc(5*sizeof(int)); //TRY to allocate 5times the dna integer to get an array
   Agent.dna[3] = 12;  //try to set a value into index 3 of the dna-array
}

typedef struct
{
	char fitness;
	int* dna;
}organism;
void main(){
	organism* Agent = sys_malloc(sizeof(organism));
	Agent.dna 		 = sys_malloc(5*sizeof(int));

	//reset your memory,make all is '\0'
	memset(Agent.dna,'\0',5);
	
	//and than set your varible
	(Agent.dna)[3] = 12; 
	printf("%d",	(Agent.dna)[3]);
		
	sys_free(Agent.dna);
	sys_free(Agent);
}

//reset your memory,make all is '\0'
memset(Agent.dna,'\0',5);

// BETTER
//reset your memory,make all is '\0'
memset(Agent.dna,0,sizeof(int) * 5); // does not need to be a character, also int is 4 byte in size

// 2D array [dim1][dim2] :

	short** myarray = NULL;
...
	myarray = (short**)sys_malloc( (int)dim1length * sizeof(short*) );
	for(i=0;i<dim1length ;i++)
		{
			myarray[i]	= (short*)sys_malloc( (int)dim2length  * sizeof(short) );
			for(j=0;j<dim2length;j++)
				{
					(myarray[i])[j] = 0;
				}
		}