// PROGRAM vector
// 配列の表示

#include "TrueBASIC.h"
int main();
void initial(double a[], double b[]);
void dot(double a[], double b[]);
void cross(double r[], double s[]);

int main()
{
    double a[4], b[4];

    initial(a, b);
    dot(a, b);
    cross(a, b);

    return 0;
}

void initial(double a[], double b[])
{
    a[1] = 2;
    a[2] = -3;
    a[3] = -4;
    b[1] = 6;
    b[2] = 5;
    b[3] = 1;
}

void dot(double a[], double b[])
{
    int i;
    double dot_product;

    dot_product = 0;
    for(i = 1; i <= 3; ++i)
    {
        dot_product += a[i]*b[i];
    }
    printf("scalar product =  %f\n", dot_product);
}

void cross(double r[], double s[])
// 配列は主プログラムやサブルーチンの中でも定義できる
// 仮の変数を用いていることに注意
{
    int component, i, j;
    double cross_product[4];

    for(component = 1; component <= 3; ++component)
    {
        i = (component % 3) + 1;
        j = (i % 3) + 1;
        cross_product[component] = r[i]*s[j] - s[i]*r[j];
    }
    printf("\n");
    printf("three components of the vector product:\n");
    printf("          x            y            z \n");
    for(component = 1; component <= 3; ++component)
        printf("%12f ", cross_product[component]);
}