C lang: VLA(variable-length array)

Xx_VLA Introduction

• VLA:variable-length array,not variable array size,but variable arary dimensionality size.
• Must be an automatic storage type
• They cannot be initialized in a declaration
• VLA is new feature,depend on compiler support.

Ax_Code

#include<stdio.h>
#define ROWS 3
#define COLS 4
int sum2d(int rows, int cols, int ar[rows][cols]);
int main(void)
{
    int i, j;
    int rs = 3;
    int cs = 10;
    int junk[ROWS][COLS] =
    {
        2, 4, 6, 8,
        3, 5, 7, 9,
        12, 10, 8, 6
    };
    int morejunk[ROWS - 1][COLS + 2] =
    {
        20, 30, 40, 50, 60, 70,
        5, 6, 7, 8, 9, 10
    };
    int vari[rs][cs];       // VLA
    for ( i = 0; i < rs; i++)
        for (j = 0; j < cs; j++)
            vari[i][j] = i * j + j;
    printf("3x5 array\n");
    printf("Sum of all elements = %d\n", sum2d(ROWS, COLS, junk));
    printf("2x6 array\n");
    printf("Sum of all elements = %d\n", sum2d(ROWS - 1, COLS + 2, morejunk));
    printf("3x10 VLA!\n");
    printf("Sum of all elements = %d\n", sum2d(rs, cs, vari));
    return 0;
}
int sum2d(int rows, int cols, int ar[rows][cols])
{
    int r;
    int c;
    int tot;
    tot = 0;
    for (r = 0; r < rows ; r++)
        for (c = 0; c < cols; c ++)
            tot = tot + ar[r][c];
    return tot;
}

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3x5 array
Sum of all elements = 80
2x6 array
Sum of all elements = 315
3x10 VLA!
Sum of all elements = 270

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END