dynamic definition of vector and matrix.

vecmat.c

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

void
print_vec(double *v, int n) {
    int i;
    for (i = 0; i < n; i++) {
        printf("vec_%d = %.4f\n", i + 1, v[i]);
    }
}

void
init_vec(double *v, int n) {
    int n5 = n % 5;
    int i;
    for (i = 0; i < n5; i++) {
        v[i] = 1.5;
    }
    for (; i < n; i+=5) {
        v[i] = 1.;
        v[i + 1] = 1.;
        v[i + 2] = 10.;
        v[i + 3] = 1.;
        v[i + 4] = 1.;
    }
}

void
print_mat(double **a, int m, int n) {
    int i, j;
    for (i = 0; i < m; i++) {
        for (j = 0; j < n; j++) {
            printf("%6.2f", a[i][j]);
        }
        printf("\n");
    }
}

void
init_mat(double **a, int m, int n) {
    int i, j;
    for (i = 0; i < m; i++) {
        for (j = 0; j < n; j++) {
            a[i][j] = i + j;
        }
    }
    // a[2][3] = -1.;
}

int
main(int argc, char* argv[]) {
    int n = 39;
    double *x = (double *)malloc(n * sizeof(double));
    double **a;
    int i;

    // mallocした最初の要素にすべての領域を確保
    a = malloc(n * sizeof(double *));
    a[0] = malloc(n * n * sizeof(double));
    for (i = 1; i < n; i++) {
        a[i] = a[0] + n * i;
    }


    init_vec(x, n);
    init_mat(a, n, n);

    print_vec(x, n);
    printf("---\n");
    print_mat(a, n, n);

    // mallocを解放する
    free(a);
    free(x);

    return 0;
}