Рабочая версия

#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <math.h>

int N=5;
typedef double (*mytype)(double, double); //тип указывающий на функцию

double f0(double x, double y)
{
    return cos(x)/x+(-1.0)*(y+0)/x;
}

double f1(double x, double y)
{
    return x/50;
}

double f2 (double x, double y)
{
    return (-2.0)* (y+2)/ x;
}

double f3 (double x, double y)
{
    return -cos(x);
}

double f4 (double x, double y)
{
    return sin (x);
}


double* StepEuler (double x, double *y, double step, int N, double (*func[])(double, double ))
{
    for (int i=0; i<N; i++)
    {
        y[i]=y[i]+func[i](x, y[i])*step;
    }
    return y;
}
double* StepRK(double x, double *y, double step, int N, double (*func[])(double, double))
{
    double *k1, *k2, *k3, *k4;
    k1 = malloc(N * sizeof(double));
    k2 = malloc(N * sizeof(double));
    k3 = malloc(N * sizeof(double));
    k4 = malloc(N * sizeof(double));

    for (int i = 0; i < N; ++i)
        k1[i] = func[i](x,y[i]);

    double *dop = malloc(N * sizeof(double));
    for (int i = 0; i < N; ++i)
    {
        dop[i] = y[i] + k1[i]*step/2;
        k2[i] = func[i]((x+step/2),(dop[i]));

    }

    for (int i = 0; i < N; ++i)
    {
        dop[i] = y[i] + k2[i]*step/2;
        k3[i] = func[i]((x+step/2),(dop[i]));

    }

    for (int i = 0; i < N; ++i)
    {
        dop[i] = y[i] + k1[i]*step;
        k4[i] = func[i]((x+step),(dop[i]));

    }

    for (int i = 0; i < N; ++i)
        y[i] = y[i]+ step*(k1[i]+2*k2[i]+2*k3[i]+k4[i])/6;

    return y;
}

void main()
{
    mytype *mass = malloc(N * sizeof(mytype));
    mass[0]=f0;
    mass[1]=f1;
    mass[2]=f2;
    mass[3]=f3;
    mass[4]=f4;
    FILE *fe, *fk;
    fe=fopen ("Euler.txt", "w");

    //double (*mass[]) (double, double*, int) ={f0, f1, f3, f2, f4};
    double x, xk, h, x0, y1, y2, y3, y4, y5;
    printf("Input interval");
    scanf("%lf%lf", &x, &xk);
    x0=x;
    printf("Input step");
    scanf("%lf", &h);
    printf("Input start conditions");
    scanf("%lf%lf%lf%lf%lf", &y1, &y2,&y3,&y4,&y5);
    double *y = malloc(N * sizeof(double));
    *y=y1;
    *(y+1)=y2;
    *(y+2)=y3;
    *(y+3)=y4;
    *(y+4)=y5;
    for (;x < xk; x =x+ h) {
        printf("%lf\t", x);
        fprintf(fe, "%lf\t", x);
        for (int i = 0; i < N; ++i) {
            printf("%lf\t", y[i]);
            fprintf(fe, "%lf\t", y[i]);
        }
        y = StepEuler(x, y, h, N, mass);
        printf("\n");
        fprintf(fe, "\n");
    }
    fclose(fe);
    *y=y1;
    *(y+1)=y2;
    *(y+2)=y3;
    *(y+3)=y4;
    *(y+4)=y5;
    x=x0;
    fk=fopen ("RK.txt", "w");
    for (;x < xk; x =x + h) {
        printf("%lf\t", x);
        fprintf(fk, "%lf\t", x);
        for (int i = 0; i < N; i++) {
            printf("%lf\t", y[i]);
            fprintf(fk, "%lf\t", y[i]);
        }
        y = StepRK(x, y, h, N, mass);
        printf("\n");
        fprintf(fk, "\n");
    }
    fclose(fe);
    fclose(fk);
}