```/* nag_mann_whitney (g08amc) Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
*
* Mark 26.1, 2017.
*/

#include <stdio.h>
#include <nag.h>
#include <nag_stdlib.h>
#include <nagg08.h>

int main(void)
{

Integer exit_status = 0, i, n1, n2;
NagError fail;
double p, u, *x = 0, *y = 0, z;

INIT_FAIL(fail);

printf("nag_mann_whitney (g08amc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT " %" NAG_IFMT " ", &n1, &n2);
printf("%s%5" NAG_IFMT "\n", "Sample size of group 1 = ", n1);
printf("%s%5" NAG_IFMT "\n", "Sample size of group 2 = ", n2);
if (!(x = NAG_ALLOC(n1, double))
|| !(y = NAG_ALLOC(n2, double)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
printf("\n");
for (i = 1; i <= n1; ++i)
scanf("%lf", &x[i - 1]);
printf("%s\n", "Mann-Whitney U test");
printf("\n");
printf("%s\n", "Data values");
printf("\n");
printf("%s", "    Group 1  ");
for (i = 1; i <= n1; ++i)
printf("%5.1f%s", x[i - 1], i % 8 ? "" : "\n             ");
for (i = 1; i <= n2; ++i)
scanf("%lf", &y[i - 1]);
printf("\n");
printf("%s", "    Group 2  ");
for (i = 1; i <= n2; ++i)
printf("%5.1f%s", y[i - 1], i % 8 ? "" : "\n             ");

/* nag_mann_whitney (g08amc).
* Performs the Mann-Whitney U test on two independent
* samples
*/
nag_mann_whitney(n1, x, n2, y, Nag_LowerTail, Nag_CompProbApprox,
&u, &z, &p, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_mann_whitney (g08amc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
printf("\n\n");
printf("%s%8.4f\n", "Test statistic                 = ", u);
printf("%s%8.4f\n", "Normal Statistic               = ", z);
printf("%s%8.4f\n", "Approximate tail probability   = ", p);
/* nag_mann_whitney (g08amc), see above. */
nag_mann_whitney(n1, x, n2, y, Nag_LowerTail, Nag_CompProbExact,
&u, &z, &p, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_mann_whitney (g08amc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
printf("%s%8.4f\n", "Exact tail probability         = ", p);
END:
NAG_FREE(x);
NAG_FREE(y);
return exit_status;
}
```