How can I pass my struct array by reference in C

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

union Data1
{
    double x1;
};
union Data2
{
    double x2;
};
struct array
{
    int n[7];
    int sums[7];
    int sumt[7];
};

double f(double x);
double simp(int n, double x1, double x2);
double trap(int n, double x1, double x2);

int main()
{
    union Data1 data1;
    union Data2 data2;
    struct array array1 = {{1,10,25,50,100,1000,10000},{0},{0}};
    int i;
    FILE *f;

    f = fopen("data.dat", "a");

    data1.x1 = -INFINITY;
    data2.x2 = INFINITY;


    printf ("Both integration techniques will run for the following intervals: 1, 10, 25, 50, 100, 1000, 10000\n");


    for(i=0;i<7;i++)
    {
    array1.sums[i] = simp(array1.n[i],data1.x1,data2.x2);
    array1.sumt[i] = trap(array1.n[i],data1.x1,data2.x2);
    }


    printf("For the trap rule:\n");
    printf("\t\tN\t\t\tSum\n");
    for(i=0;i<7;i++)
    {
       printf("\t\t%d\t\t\t%d\n",array1.n[i],array1.sumt[i]);
    }

    printf("For the simpson rule:\n");
    printf("\t\tN\t\t\tSum\n");
    for(i=0;i<7;i++)
    {
       printf("\t\t%d\t\t\t%d\n",array1.n[i],array1.sums[i]);
    }

    fprintf(f, "For the simpson rule:\n");
    fprintf(f,"\t\tN\t\t\tSum\n");
    for(i=0;i<7;i++)
    {
       fprintf(f,"\t\t%d\t\t\t%d\n",array1.n[i],array1.sums[i]);

    }
    fprintf(f,"For the trap rule:\n");
    fprintf(f,"\t\tN\t\t\tSum\n");
    for(i=0;i<7;i++)
    {
       fprintf(f,"\t\t%d\t\t\t%d\n",array1.n[i],array1.sumt[i]);
    }
    fclose(f);

    return 0;

}

double f(double x)
{
    double y;

    y = exp(-pow(x,2));

    return y;
}

double simp(int n, double a, double b)
{
    int i;
    double dx, x, sum;

    dx = (b-a)/n;
    sum = f(a)+ f(b);
    for(i=1;i<n;i++)
    {
        x = a + dx*i;
        sum += 2*(1+i%2)*f(x);
    }
    sum*=dx/3;
    return sum;
}

double trap(int n, double a, double b)
{
    int i;
    double dx, x, sum;

    dx=(b-a)/n;
    sum = f(a)+f(b);
    for(i=1;i<n;i++)
    {
        x = a + dx*i;
        sum += 2*f(x);
    }

    sum *= dx/2;
    return sum;
}