v0.40: Create exercises. Challenge the community.

reverse_int

Your mission

Implement a function that reverses the order of the first n elements of an integer array in place, without allocating a second array.

See it in action

int a[] = {1, 2, 3}; reverse_int(a, 3);

Expected result

3 2 1

Your checklist

For your own tracking. Tests grade your code.

a points to the first element of a mutable array, and n is how many leading elements you must reverse.
Swap the front element with the back one, then step both cursors toward the middle until they meet or cross.
Work in place: no temporary array of n elements, no copy. A single int to hold a value during a swap is fine.
There is no terminator here, unlike a string. n is the only thing that tells you where the region ends.
An n of 0 leaves the array exactly as it was. An odd n keeps the middle element in place.
When n is smaller than the real length of the array, only that prefix is reversed and every element after it stays where it was.
The tests print the array after the call: values on one line, separated by a single space, followed by a newline.

More examples

int a[] = {1, 2, 3, 4, 5}; reverse_int(a, 3);

Expected result

3 2 1 4 5

int a[] = {7, 8, 9}; reverse_int(a, 0);

Expected result

7 8 9

Constraints

Expected files

reverse_int.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

reverse_int

Arrays and matrices

Your mission

Implement a function that reverses the order of the first n elements of an integer array in place, without allocating a second array.

See it in action

int a[] = {1, 2, 3}; reverse_int(a, 3);

Expected result

3 2 1

Your checklist

For your own tracking. Tests grade your code.

a points to the first element of a mutable array, and n is how many leading elements you must reverse.
Swap the front element with the back one, then step both cursors toward the middle until they meet or cross.
Work in place: no temporary array of n elements, no copy. A single int to hold a value during a swap is fine.
There is no terminator here, unlike a string. n is the only thing that tells you where the region ends.
An n of 0 leaves the array exactly as it was. An odd n keeps the middle element in place.
When n is smaller than the real length of the array, only that prefix is reversed and every element after it stays where it was.
The tests print the array after the call: values on one line, separated by a single space, followed by a newline.

More examples

int a[] = {1, 2, 3, 4, 5}; reverse_int(a, 3);

Expected result

3 2 1 4 5

int a[] = {7, 8, 9}; reverse_int(a, 0);

Expected result

7 8 9

Constraints

Expected files

reverse_int.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

01Even count reverses fullyWaiting

02Odd count keeps the middle elementWaiting

03Five elements around a fixed centerWaiting

04Two elements swapWaiting

05Single element stays putWaiting

06Zero length leaves the array intactWaiting

07All values negativeWaiting

08Negatives, zero and positives mixedWaiting

09Identical values look unchangedWaiting

10Ten elementsWaiting

11Only the first n elements moveWaiting

12A prefix of one changes nothingWaiting

13Holds INT_MIN and INT_MAXWaiting

14Two reversals restore the original orderWaiting

reverse_int

Your mission

Implement a function that reverses the order of the first n elements of an integer array in place, without allocating a second array.

See it in action

int a[] = {1, 2, 3}; reverse_int(a, 3);

Expected result

3 2 1

Your checklist

For your own tracking. Tests grade your code.

a points to the first element of a mutable array, and n is how many leading elements you must reverse.
Swap the front element with the back one, then step both cursors toward the middle until they meet or cross.
Work in place: no temporary array of n elements, no copy. A single int to hold a value during a swap is fine.
There is no terminator here, unlike a string. n is the only thing that tells you where the region ends.
An n of 0 leaves the array exactly as it was. An odd n keeps the middle element in place.
When n is smaller than the real length of the array, only that prefix is reversed and every element after it stays where it was.
The tests print the array after the call: values on one line, separated by a single space, followed by a newline.

More examples

int a[] = {1, 2, 3, 4, 5}; reverse_int(a, 3);

Expected result

3 2 1 4 5

int a[] = {7, 8, 9}; reverse_int(a, 0);

Expected result

7 8 9

Constraints

Expected files

reverse_int.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

v0.40: Create exercises. Challenge the community.

Meet Studio →

reverse_int

Arrays and matrices

Your mission

Implement a function that reverses the order of the first n elements of an integer array in place, without allocating a second array.

See it in action

int a[] = {1, 2, 3}; reverse_int(a, 3);

Expected result

3 2 1

Your checklist

For your own tracking. Tests grade your code.

a points to the first element of a mutable array, and n is how many leading elements you must reverse.
Swap the front element with the back one, then step both cursors toward the middle until they meet or cross.
Work in place: no temporary array of n elements, no copy. A single int to hold a value during a swap is fine.
There is no terminator here, unlike a string. n is the only thing that tells you where the region ends.
An n of 0 leaves the array exactly as it was. An odd n keeps the middle element in place.
When n is smaller than the real length of the array, only that prefix is reversed and every element after it stays where it was.
The tests print the array after the call: values on one line, separated by a single space, followed by a newline.

More examples

int a[] = {1, 2, 3, 4, 5}; reverse_int(a, 3);

Expected result

3 2 1 4 5

int a[] = {7, 8, 9}; reverse_int(a, 0);

Expected result

7 8 9

Constraints

Expected files

reverse_int.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

01Even count reverses fullyWaiting

02Odd count keeps the middle elementWaiting

03Five elements around a fixed centerWaiting

04Two elements swapWaiting

05Single element stays putWaiting

06Zero length leaves the array intactWaiting

07All values negativeWaiting

08Negatives, zero and positives mixedWaiting

09Identical values look unchangedWaiting

10Ten elementsWaiting

11Only the first n elements moveWaiting

12A prefix of one changes nothingWaiting

13Holds INT_MIN and INT_MAXWaiting

14Two reversals restore the original orderWaiting