C code for Runge Kutta

The below code is for Runge Kutta 4th order

#include<stdio.h>

float equation(float x,float y)

{

    float z;

    z=x-y;

    return z;

}

void main()

{

 float y,x,h,k,k1,k2,k3,k4,f1,f2,f3,f4,n,m,i;

    printf("Enter initial value of x:");

    scanf("%f",&x);

    printf("Enter initial value of y:");

    scanf("%f",&y);

    printf("Enter Interval Size:");

    scanf("%f",&h);

    printf("Enter value to be found:");

    scanf("%f",&n);

    m=n/h;

    for(i=1;i<=m;i++)

    {

        f1=equation(x,y);

        k1=h*f1;

        f2=equation(x+(h/2),y+(k1/2));

        k2=h*f2;

        f3=equation(x+(h/2),y+(k2/2));

        k3=h*f3;

        f4=equation(x+h,y+k3);

        k4=h*f4;       

        k=(k1+(2*k2)+(2*k3)+k4)/6;

        x=x+h;

        y=y+k;

    }   

    printf("\ny(%f)=%f\n",n,y);

}