rev

The rev Command

rev reverses each line of its input. Each line is printed backwards; the line order stays the same.

$ echo "hello" | rev
olleh

$ printf "cat\ndog\n" | rev
tac
god

Your Implementation

Write void my_rev(const char *s) that reverses each line.

The algorithm: scan forward through the string. When you hit a \n (or end of string), you know where the current line ends. Walk backwards from end to start, printing each character, then print the newline.

void my_rev(const char *s) {
    const char *line_start = s;

    while (*s) {
        if (*s == '\n') {
            // Print characters from (s-1) down to line_start
            const char *p = s - 1;
            while (p >= line_start) {
                putchar(*p);
                p--;
            }
            putchar('\n');
            line_start = s + 1;
        }
        s++;
    }
}

Pointer Arithmetic

This lesson is about pointer arithmetic — a core C skill:

• const char *line_start = s — pointer to the start of the current line
• const char *p = s - 1 — pointer one character before the \n
• p-- — move the pointer one character earlier
• p >= line_start — stop when we have passed the start

Pointers and array indices are interchangeable in C: p[0] and *p are the same thing.

Your Task

Implement my_rev so it prints each line reversed.