Victim-predator

Task9

#define _CRT_SECURE_NO_DEPRECATE
#include "stdio.h"
#include "math.h"
#include "conio.h"
#include <iostream>

int a = 10;
int b = 2;
int c = 2;
int d = 10;

double U(double t,double x,double y)
{
	return a*x - b*x*y;
}
double V(double t,double x,double y)
{
	return c*x*y - d*y;
}
void solve()
{
	double t = 0;
	double step = 0.001;

	double x = 4.99;
	double y = 5.01;

	double q0, q1, q2, q3;
	double k0, k1, k2, k3;

	FILE * file;
	file = fopen("file.txt", "w");

	while (t < 10.0)
	{
		fprintf(file, "%.8e %.8e %.8e\n", t, x , y);
		q0 = U(t, x, y);
		k0 = V(t, x, y);

		q1 = U(t+step/2.0,x+k0*step/2.0, y+q0*step/2.0);
		k1 = V(t+step/2.0,x+k0*step/2.0, y+q0*step/2.0);

		q2 = U(t+step/2.0,x+k1*step/2.0, y+q1*step/2.0);
		k2 = V(t+step/2.0,x+k1*step/2.0, y+q1*step/2.0);

		q3 = U(t+step,x+k2*step, y+q2*step);
		k3 = V(t+step,x+k2*step, y+q2*step);

		x = x + step*(k0+2.0*k1+2.0*k2+k3)/6.0;
		y = y + step*(q0+2.0*q1+2.0*q2+k3)/6.0;

		t = t + step;
	}
	fclose(file);
}

void main()
{
	solve();
	getchar();
	return;
}