row_sums

Arrays and matrices16

Objective

Write a function that fills an output array with the sum of each row of a 2D grid whose rows are exactly four integers wide.

Steps

rows points at the first row of the grid, nrows is how many rows to read, and out points at a buffer with room for nrows values of type int.
Set out[i] to rows[i][0] + rows[i][1] + rows[i][2] + rows[i][3].
The width is fixed at 4 by the type itself, not by a parameter. const int (*rows)[4] is a pointer to an array of 4 int, so rows[i][j] reads column j of row i, and rows + 1 walks forward by four whole int in one step. An int ** would be a different animal: an array of pointers, each aiming at a row that can live anywhere in memory.
The grid is one contiguous block of nrows * 4 integers. Row i begins at offset i * 4 inside that block.
Write exactly nrows values into out, never more.
When nrows is 0, leave out untouched and return.
Treat rows as read-only. Never write through it.
Every row sum fits in an int, so plain int arithmetic is enough.
The checker prints the values of out on one line, separated by a single space, with a trailing newline.

examples

$ int grid[2][4] = {{1, 2, 3, 4}, {5, 6, 7, 8}}; row_sums(grid, 2, out);

10 26

$ int grid[3][4] = {{1, 2, 3, 4}, {10, 20, 30, 40}, {100, 200, 300, 400}}; row_sums(grid, 3, out);

10 100 1000

$ int out[3] = {-1, -1, -1}; row_sums(grid, 0, out);

-1 -1 -1

Constraints

Expected files

row_sums.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

Tests

Run the tests to grade your code

Build

01One row of four values

02Two rows

03Three rows

04Zero rows leaves out untouched

05Only the first nrows slots are written

06Each row is four int further along

07Rows of negative values

08Only zeros

09Positive and negative values in the same row

10A row that cancels itself out

11Five rows

12Six rows with a single set value each

13Sums that reach the edges of an int

14The grid is left as it was

row_sums

Objective

Write a function that fills an output array with the sum of each row of a 2D grid whose rows are exactly four integers wide.

Steps

rows points at the first row of the grid, nrows is how many rows to read, and out points at a buffer with room for nrows values of type int.
Set out[i] to rows[i][0] + rows[i][1] + rows[i][2] + rows[i][3].
The width is fixed at 4 by the type itself, not by a parameter. const int (*rows)[4] is a pointer to an array of 4 int, so rows[i][j] reads column j of row i, and rows + 1 walks forward by four whole int in one step. An int ** would be a different animal: an array of pointers, each aiming at a row that can live anywhere in memory.
The grid is one contiguous block of nrows * 4 integers. Row i begins at offset i * 4 inside that block.
Write exactly nrows values into out, never more.
When nrows is 0, leave out untouched and return.
Treat rows as read-only. Never write through it.
Every row sum fits in an int, so plain int arithmetic is enough.
The checker prints the values of out on one line, separated by a single space, with a trailing newline.

examples

$ int grid[2][4] = {{1, 2, 3, 4}, {5, 6, 7, 8}}; row_sums(grid, 2, out);

10 26

$ int grid[3][4] = {{1, 2, 3, 4}, {10, 20, 30, 40}, {100, 200, 300, 400}}; row_sums(grid, 3, out);

10 100 1000

$ int out[3] = {-1, -1, -1}; row_sums(grid, 0, out);

-1 -1 -1

Constraints

Expected files

row_sums.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

row_sums

Arrays and matrices16

Objective

Write a function that fills an output array with the sum of each row of a 2D grid whose rows are exactly four integers wide.

Steps

rows points at the first row of the grid, nrows is how many rows to read, and out points at a buffer with room for nrows values of type int.
Set out[i] to rows[i][0] + rows[i][1] + rows[i][2] + rows[i][3].
The width is fixed at 4 by the type itself, not by a parameter. const int (*rows)[4] is a pointer to an array of 4 int, so rows[i][j] reads column j of row i, and rows + 1 walks forward by four whole int in one step. An int ** would be a different animal: an array of pointers, each aiming at a row that can live anywhere in memory.
The grid is one contiguous block of nrows * 4 integers. Row i begins at offset i * 4 inside that block.
Write exactly nrows values into out, never more.
When nrows is 0, leave out untouched and return.
Treat rows as read-only. Never write through it.
Every row sum fits in an int, so plain int arithmetic is enough.
The checker prints the values of out on one line, separated by a single space, with a trailing newline.

examples

$ int grid[2][4] = {{1, 2, 3, 4}, {5, 6, 7, 8}}; row_sums(grid, 2, out);

10 26

$ int grid[3][4] = {{1, 2, 3, 4}, {10, 20, 30, 40}, {100, 200, 300, 400}}; row_sums(grid, 3, out);

10 100 1000

$ int out[3] = {-1, -1, -1}; row_sums(grid, 0, out);

-1 -1 -1

Constraints

Expected files

row_sums.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

Tests

Run the tests to grade your code

Build

01One row of four values

02Two rows

03Three rows

04Zero rows leaves out untouched

05Only the first nrows slots are written

06Each row is four int further along

07Rows of negative values

08Only zeros

09Positive and negative values in the same row

10A row that cancels itself out

11Five rows

12Six rows with a single set value each

13Sums that reach the edges of an int

14The grid is left as it was