print_value.c

#include <stdio.h>

//Implements a If() that works just like if in C
//Defines a function pointer type for our callback function
typedef void(*ConditionBranchFunc)(void* val);

//This If() takes in 4 parameters, tFunc is the function called when
// condition == 1. fFunc is called when condition == 0. condition is
// weathere the statement is true or false. dataPtr is a pointer that
// points to a data structure passed to tFunc and fFunc.
void If(ConditionBranchFunc tFunc, ConditionBranchFunc fFunc
	, int condition, void* dataPtr)
{
	ConditionBranchFunc func[2] = {fFunc,tFunc};
	ConditionBranchFunc execFunc = func[condition];
	execFunc(dataPtr);
}

//Prints an integer that is pointed by the pointer
void printInt(void* intPtr)
{
	printf("%d\n",*(int*)intPtr);
}

//Does nothing
void foo(void* ptr)
{
}

//A structure that stores the data for the current state of executtion
// of the printing
typedef struct
{
	int minVal;
	int maxVal;
} Data;

//Dose the job of printing from maxVal to minVal
void executePrint(void* dataPtr)
{
	Data dat;
	Data* data = (Data*)dataPtr;
	dat.minVal = data->minVal;
	dat.maxVal = data->maxVal - 1;
	If(printInt,foo,data->maxVal != 0,&(data->maxVal));
	If(executePrint,foo,data->maxVal != 0,&dat);

}

//Swaps the value in the data structure passed in then print
void swapAndExecute(void* dataPtr)
{
	Data* data = (Data*)dataPtr;
	Data dat;
	dat.minVal = data->maxVal;
	dat.maxVal = data->minVal;
	executePrint(&dat);
}

//The interface function. As the assignment requires
void p(int a, int b)
{
	Data data;
	data.minVal = b;
	data.maxVal = a;
	If(executePrint,swapAndExecute,a>b,&data);
}

int main()
{
	p(5,1);
	return 0;
}