row_sums

Arrays and matrices

Your mission

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.

See it in action

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

Expected result

10 26

Your checklist

For your own tracking. Tests grade your code.

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.

More examples

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

Expected result

10 100 1000

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

Expected result

-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 your code, then check each test here. Open a result to inspect its output.

Build

01One row of four valuesWaiting

02Two rowsWaiting

03Three rowsWaiting

04Zero rows leaves out untouchedWaiting

05Only the first nrows slots are writtenWaiting

06Each row is four int further alongWaiting

07Rows of negative valuesWaiting

08Only zerosWaiting

09Positive and negative values in the same rowWaiting

10A row that cancels itself outWaiting

11Five rowsWaiting

12Six rows with a single set value eachWaiting

13Sums that reach the edges of an intWaiting

14The grid is left as it wasWaiting

row_sums

Your mission

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.

See it in action

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

Expected result

10 26

Your checklist

For your own tracking. Tests grade your code.

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.

More examples

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

Expected result

10 100 1000

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

Expected result

-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 matrices

Your mission

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.

See it in action

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

Expected result

10 26

Your checklist

For your own tracking. Tests grade your code.

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.

More examples

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

Expected result

10 100 1000

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

Expected result

-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 your code, then check each test here. Open a result to inspect its output.

Build

01One row of four valuesWaiting

02Two rowsWaiting

03Three rowsWaiting

04Zero rows leaves out untouchedWaiting

05Only the first nrows slots are writtenWaiting

06Each row is four int further alongWaiting

07Rows of negative valuesWaiting

08Only zerosWaiting

09Positive and negative values in the same rowWaiting

10A row that cancels itself outWaiting

11Five rowsWaiting

12Six rows with a single set value eachWaiting

13Sums that reach the edges of an intWaiting

14The grid is left as it wasWaiting