path: root/ch1/reverse.c

#include<stdio.h>

#define MAXLENGTH 1000

// Prototypes
int get_line(char line[], int maxlength);
void line_copy(char to[], char from[]);
void reverse_copy(char to[], char from[], int length);

/*
 * MAIN
 * Reverse all lines on STDIN.
 */
int main() {
    int len; // current line length
    char line[MAXLENGTH]; // current input line
    char reversed_line[MAXLENGTH]; // current reversed line

    while ((len = get_line(line, MAXLENGTH)) > 0) {
        reverse_copy(reversed_line, line, len);
        printf("%s\n", reversed_line);
    }
    return 0;
}

/*
 * GET_LINE
 * Read STDIN into LINE up to MAXLENGTH.
 * Returns the length of LINE.
 */
int get_line(char line[], int maxlength) {
    int c, i;

    for (i = 0; i < maxlength - 1 && (c = getchar()) != EOF && c != '\n'; ++i)
        line[i] = c;
    if (c == '\n') {
        line[i] = c;
        ++i;
    }
    line[i] = '\0';
    return i;
}

/*
 * LINE_COPY
 * Copy FROM into TO; assume TO is big enough.
 */
void line_copy(char to[], char from[]) {
    int i;

    i = 0;
    while ((to[i] = from[i]) != '\0')
        ++i;
}

/*
 * REVERSE_COPY
 * Copy FROM into TO (of length LENGTH) in reverse order; assume TO is big
 * enough.
 */
void reverse_copy(char to[], char from[], int length) {
    int i;

    for (i = 0; i < length; ++i) {
        to[length - 1 - i] = from[i];
    }

    to[length] = '\0';
}