hello.any one advanced in runge kutta 4th order and c programing? Am just an undergraduate working on it. I need help with this code. It sussessfully solves a system of differential equations using runge kutta 4th order, but my lecturer wants something else. something i dont know how to do. the code originally has the question already in the program, but what am required to do is make the program ask the question like an interface asking the question and parameters to solve. i believe u will understand when i post the code.


‪#‎define‬ X0 1.0
#define Xn 2.0
#define STEPLEN 10
#define Y1 1 //initial condition for y1 at x=0
#define Y2 0 //initial condition for y2 at x=0
‪#‎include‬ <stdio.h>
#include <math.h>
#include <stdlib.h>
double f1(double x,double y1,double y2)
{
//a function to solve the functions 2 using x and y
return(y2);
}
double f2(double x,double y1,double y2)
{
//a function to solve the functions 1 using x and y
return(x*log(x) - (2*y1)/(x*x) + (2*y2)/x);
}
main()
{
double x,y1[STEPLEN],y2[STEPLEN];
double xmid,k1[2],k2[2],k3[2],k4[2],h = (double)(Xn - X0)/STEPLEN;
x = X0;
y1[0]=Y1;
y2[0]=Y2;
int i;
printf("This are the initial values. y1=%.10f y2=%.10f and h=%f\n\n", y1[0], y2[0],h);
//printf("x\t|k1\t|k2\t|k3\t|k4\t|y\n\n";
for(i=0; i<STEPLEN; i++){
k1[0]=h * f1(x,y1[i],y2[i]);
k1[1]=h * f2(x,y1[i],y2[i]);
xmid = x + h/2.0;
k2[0] = h * f1(xmid, y1[i] + k1[0] * 1/2.0, y2[i] + k1[1] * 1/2.0);
k2[1] = h * f2(xmid, y1[i] + k1[0] * 1/2.0, y2[i] + k1[1] * 1/2.0);
k3[0] = h * f1(xmid, y1[i] + k2[0] * 1/2.0, y2[i] + k2[1] * 1/2.0);
k3[1] = h * f2(xmid, y1[i] + k2[0] * 1/2.0, y2[i] + k2[1] * 1/2.0);

k4[0] = h * f1(x + h, y1[i] + k3[0] , y2[i] + k3[1]);
k4[1] = h * f2(x + h, y1[i] + k3[0] , y2[i] + k3[1]);

y1[i+1] = y1[i] + (k1[0] + 2*k2[0] + 2*k3[0] + k4[0])/6;

y2[i+1] = y2[i] + (k1[1] + 2*k2[1] + 2*k3[1] + k4[1])/6;

printf("When x=%f\n",x+h);
printf("k1 for y1=%.10f\n",k1[0]);
printf("k1 for y2=%.10f\n",k1[1]);
printf("k2 for y1=%.10f\n",k2[0]);
printf("k2 for y2=%.10f\n",k2[1]);
printf("k3 for y1=%.10f\n",k3[0]);
printf("k3 for y2=%.10f\n",k3[1]);
printf("k4 for y1=%.10f\n",k4[0]);
printf("k4 for y2=%.10f\n",k4[1]);
printf("y1 when x is %f=\t%.10f\n",x+h,y1[i+1]);
printf("y2 when x is %f=\t%.10f\n\n",x+h,y2[i+1]);
// printf("%f %f %f %f %f %f %f %f %f %f \n",k1[0],k1[1],k2[0],k2[1],k3[0],k3[1],k4[0],k4[1],y1[i+1],y2[i+1]);
x = x+h;

}
system("pause";
}
please if u dont mind contact me by email @ afotrick2011@gmail.com Please. your help will be very much apprciated.

Do you mean GUI or just want the program to ask for input( you can use scanf function)?