Euler + Runge

Task8

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

double step = 0.1;

double function(double t, double x)
{
	if (t == 0)
		return 1.0;
	if (t < 0)
		return -1;
	return -x;
}

double get_x(double prev_t, double prev_x)
{
	if (prev_t == 0)
		return 1.0;
	return prev_x + step * function(prev_t,prev_x);
}

void euler()
{
	double t = 0.0	
	double x = 0.0;
	
	FILE * file;
	file = fopen("file.txt", "w");

	while (t < 3.0)
	{
		fprintf(file, "%.8e %.8e\n", t, x = get_x(t, x));
		t = t + step;
	}

	fclose(file);
}

void runge()
{
	double t = 0.0
	double x = 0.0;
	double z;
	x = function(t,x);

	FILE * file;
	file = fopen("file2.txt", "w");
	fprintf(file, "%.8e %.8e\n", t, x);

	while (t < 3)
	{
		z = x + step * function(t , x);
		x = x + step / 2 * (function(t , x) + function(t += step, z));
		fprintf(file, "%.8e %.8e\n", t, x);
	}
	fclose(file);
}

void main()
{
	euler();
	runge();
	getchar();
}