v0.40: Create exercises. Challenge the community.

strncmp

Your mission

Implement gm_strncmp, your own strncmp, which compares two null-terminated strings, but never looks at more than the first n bytes.

See it in action

gm_strncmp("ab", "abc", 2)

Expected result

Your checklist

For your own tracking. Tests grade your code.

Scan both strings together, byte by byte, while the index is below n.
Stop as soon as a byte differs, or as soon as you reach a \0 in either string, even if that happens before n.
Compare each byte as an unsigned char, so bytes with the high bit set rank above ordinary ASCII.
Return 0 when the compared bytes all match, a negative value when the first differing byte in s1 is smaller, and a positive value when it is larger.
When n is 0, compare nothing and return 0.
Only the sign of the result is meaningful; do not call any library function.

More examples

gm_strncmp("ab", "abc", 3)

Expected result

negative value

Constraints

Expected files

strncmp.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

libc

Standard C library

Implements the contract of a function from the standard C library.

strncmp

Writing text without overflowing

Your mission

Implement gm_strncmp, your own strncmp, which compares two null-terminated strings, but never looks at more than the first n bytes.

See it in action

gm_strncmp("ab", "abc", 2)

Expected result

Your checklist

For your own tracking. Tests grade your code.

Scan both strings together, byte by byte, while the index is below n.
Stop as soon as a byte differs, or as soon as you reach a \0 in either string, even if that happens before n.
Compare each byte as an unsigned char, so bytes with the high bit set rank above ordinary ASCII.
Return 0 when the compared bytes all match, a negative value when the first differing byte in s1 is smaller, and a positive value when it is larger.
When n is 0, compare nothing and return 0.
Only the sign of the result is meaningful; do not call any library function.

More examples

gm_strncmp("ab", "abc", 3)

Expected result

negative value

Constraints

Expected files

strncmp.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

libc

Standard C library

Implements the contract of a function from the standard C library.

Tests

Run the tests to grade your code

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

Build

01Identical strings within nWaiting

02Zero length compares nothingWaiting

03First differs and is smallerWaiting

04First differs and is largerWaiting

05Equal prefix, n stops before the differenceWaiting

06Shorter string runs out firstWaiting

07n longer than the equal stringsWaiting

08Stops at NUL, ignores bytes after itWaiting

09High byte ranks above low byteWaiting

strncmp

Your mission

Implement gm_strncmp, your own strncmp, which compares two null-terminated strings, but never looks at more than the first n bytes.

See it in action

gm_strncmp("ab", "abc", 2)

Expected result

Your checklist

For your own tracking. Tests grade your code.

Scan both strings together, byte by byte, while the index is below n.
Stop as soon as a byte differs, or as soon as you reach a \0 in either string, even if that happens before n.
Compare each byte as an unsigned char, so bytes with the high bit set rank above ordinary ASCII.
Return 0 when the compared bytes all match, a negative value when the first differing byte in s1 is smaller, and a positive value when it is larger.
When n is 0, compare nothing and return 0.
Only the sign of the result is meaningful; do not call any library function.

More examples

gm_strncmp("ab", "abc", 3)

Expected result

negative value

Constraints

Expected files

strncmp.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

libc

Standard C library

Implements the contract of a function from the standard C library.

v0.40: Create exercises. Challenge the community.

Meet Studio →

strncmp

Writing text without overflowing

Your mission

Implement gm_strncmp, your own strncmp, which compares two null-terminated strings, but never looks at more than the first n bytes.

See it in action

gm_strncmp("ab", "abc", 2)

Expected result

Your checklist

For your own tracking. Tests grade your code.

Scan both strings together, byte by byte, while the index is below n.
Stop as soon as a byte differs, or as soon as you reach a \0 in either string, even if that happens before n.
Compare each byte as an unsigned char, so bytes with the high bit set rank above ordinary ASCII.
Return 0 when the compared bytes all match, a negative value when the first differing byte in s1 is smaller, and a positive value when it is larger.
When n is 0, compare nothing and return 0.
Only the sign of the result is meaningful; do not call any library function.

More examples

gm_strncmp("ab", "abc", 3)

Expected result

negative value

Constraints

Expected files

strncmp.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

libc

Standard C library

Implements the contract of a function from the standard C library.

Tests

Run the tests to grade your code

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

Build

01Identical strings within nWaiting

02Zero length compares nothingWaiting

03First differs and is smallerWaiting

04First differs and is largerWaiting

05Equal prefix, n stops before the differenceWaiting

06Shorter string runs out firstWaiting

07n longer than the equal stringsWaiting

08Stops at NUL, ignores bytes after itWaiting

09High byte ranks above low byteWaiting