Error in executing functions in C using R API

I am trying to perform numerical analysis and optimization in C using the functions made available via the R API. I am making use of the functions mentioned in the "6.7 Numerical analysis subroutines" (https://cran.r-project.org/doc/manuals/r-release/R-exts.html#Numerical-analysis-subroutines) and "6.8 Optimization" (https://cran.r-project.org/doc/manuals/r-release/R-exts.html#Optimization) sections of the "Writing R Extensions" document.

Everything is working fine except the optimization part. I do not get any error while compiling the code into a .exe file. But when I run the generated .exe file, it shuts down instantly despite adding getch() command. The complete code is given below -

#include <stdio.h>
#include <stdlib.h>
#include <Rmath.h>
#include "R_ext/Applic.h"
#include <conio.h>

typedef struct 
{
    double *X;
    int n;
} data;

double myfunc(int m, double *par, void *ex)
{
    data *input = ex;
    double *X = input->X;
    int n = input->n;
    double mu = par[0];
    double sum = 0.0;
    int i;

    for (i=0; i<n; i++) 
    {
      double t = X[i] - mu;
      sum += t*t;
    }
    return sum;
}

int main()
{
    printf("%lf\n",norm_rand());
    printf("%lf\n\n",unif_rand());

    double z = 10;
    double mean = 0;
    double sigma = 1;
    int give_log = 1;
    double result;
    result = dnorm(z,mean,sigma,give_log);
    printf("%lf\n\n",result);
    printf("%lf\n\n",gammafn(z));
    
    int i,n=1, trace=1, maxit=100, fail, fncount;
    double *par, abstol=0.0001, intol=.0001, alpha=1, beta=.5, gamma=2, *xin, *x, Fmin;
    data ex;
    par=malloc(n*sizeof(double));
    xin=malloc(n*sizeof(double));
    x=malloc(n*sizeof(double));
    par[0]=5;
    xin[0]=5;
    ex.n=5;
    ex.X=malloc(ex.n*sizeof(double));
    for(i=0;i<ex.n;i++) ex.X[i]=i;
    nmmin(n,xin,x,&Fmin,myfunc,&fail,abstol,intol,&ex,alpha,beta,gamma,trace,&fncount,maxit);
    free(par);
    free(x);
    free(xin);
    free(ex.X);
    
    getch();
    return 0;
}

Here is the output just before shutting down -

I am definitely making a mistake somewhere but don't know exactly where. Also, how can I obtain the output from the nmmin() function as its return type is void?