uniq

The uniq Command

uniq removes consecutive duplicate lines. Only adjacent duplicates are removed — non-adjacent duplicates are kept:

$ printf "apple\napple\nbanana\nbanana\napple\n" | uniq
apple
banana
apple

The first two apple lines collapse into one. The final apple stays because it is not adjacent to another apple.

Your Implementation

Write void my_uniq(const char *s) that prints deduplicated lines.

You need to remember the previous line and compare it to the current one. If they are different, print the current line. If they are the same, skip it.

void my_uniq(const char *s) {
    char prev[256];
    char line[256];
    prev[0] = '\0';

    while (*s) {
        char *out = line;
        while (*s && *s != '\n') { *out++ = *s++; }
        *out = '\0';
        if (*s == '\n') s++;

        // Compare line with prev using pointer arithmetic
        const char *a = line, *b = prev;
        while (*a && *a == *b) { a++; b++; }
        if (*a != *b) {
            printf("%s\n", line);
            // Copy line into prev
            char *d = prev;
            const char *c = line;
            while (*c) *d++ = *c++;
            *d = '\0';
        }
    }
}

Pointer-based String Compare and Copy

Instead of strcmp and strcpy from <string.h>, we compare and copy with pointer loops:

• Compare: walk both pointers together until a mismatch or end. If the final characters differ, the strings differ.
• Copy: walk src and write each character to dest until the null terminator.

This is exactly what strcmp and strcpy do internally — writing them yourself is great practice.

Your Task

Implement my_uniq that removes consecutive duplicate lines.