Final Project: mini-grep — substring match in lines

Challenge

Count how many lines of in-memory text contain a given substring — the heart of a fixed-string grep.

Task

Implement int grep_count(const char *needle, const char *haystack) that returns the number of lines in haystack that contain needle as a substring.

Input

• needle: the substring to look for (NUL-terminated).
• haystack: NUL-terminated text whose lines are separated by '\n'. The final line may be unterminated.

Output

The count of matching lines, as an int.

Example

grep_count("foo", "foo\nbar\nfoobar\n")   ->   2
grep_count("xyz", "aaa\nbbb")              ->   0
grep_count("end", "just one end")          ->   1

Edge cases

• Empty haystack: 0.
• Empty needle: every line matches (each line "contains" the empty string).
• Final line without a trailing newline still counts.

Why this matters

grep is the second-most-used UNIX tool after ls. Implementing a no-regex 'fixed string' variant teaches buffer scanning and line iteration without needing the full regex engine.

Input format

needle: substring to find. haystack: NUL-terminated text, lines split by '\n'.

Output format

int — number of lines containing needle.

Constraints

O(haystack * needle) substring search is fine.

Starter code

int grep_count(const char *needle, const char *haystack) { /* TODO */ return 0; }

Common mistakes

Treating consecutive newlines as one line; missing the last line when no trailing newline; double-counting when the needle spans a newline.

Edge cases to handle

Empty haystack: 0. Empty needle: every line matches.

Complexity

O(haystack * needle) with naive substring search.

Background lessons

• Searching for a substring
• Log parsing — line iteration + classification