ex1-19.c

#include <stdio.h>

#define BUF_SIZE 256

void reverse(char dst[], char src[], int len);
int strend(char string[], int len);
int getline(char line[], int maxline);

int main(void) {
    int len;
    char line[BUF_SIZE], rev[BUF_SIZE];

    while ( (len = getline(line, BUF_SIZE)) > 0 ) {
        if (line[0] == '\n') {
            printf("\n");
            continue;
        }

        reverse(rev, line, BUF_SIZE);
        printf("%s", rev);
    }

    return 0;
}

void reverse(char dst[], char src[], int len) {
    int i, j, end;

    end = strend(src, len);
    if (src[end] == '\n')
        dst[end] = src[end];

    for (i = 0, j = (end - 1); j >= 0; i++, j--) {
        dst[i] = src[j];
    }

    dst[++i] = '\0';
}

int strend(char string[], int len) {
    int i;

    for (i = 0; i < len; ++i) {
        if (string[i] == '\0')
            return (i-1); // -1 for "human" end of string (before '\0')
    }

    return 0;
}

int getline(char line[], int maxline) {
    int c, i;

    for (i = 0; i < (maxline-1) && (c = getchar()) != EOF && c != '\n'; ++i)
        line[i] = c;

    if (c == '\n') {
        line[i] = '\n';
        ++i;
    }

    line[i] = '\0';
    return i;
}