ex1-18.c

#include <stdio.h>

#define MAXLINE     1000
#define NEWLINE_ON  1
#define NEWLINE_OFF 0

int strend(char string[], int len);
int getline(char line[], int maxline);

int main(void) {
    int len, end, newline, count;
    char line[MAXLINE];

    count = 0;
    newline = NEWLINE_OFF;

    while ( (len = getline(line, MAXLINE)) > 0 ) {
        if (line[0] == '\n')
            continue;

        for (end = strend(line, MAXLINE); end >= 0; --end) {
            if (line[end] == '\n') {
                // Set newline to NEWLINE_ON so we can append a newline later
                newline = NEWLINE_ON;
                line[end] = '\0';
            } else if (line[end] == ' ' || line[end] == '\t') {
                // Null terminate trailing whitespace or tabs
                line[end] = '\0';
                ++count;
            } else {
                // We've reached non-trailing whitespace/tab, so we're finished
                break;
            }
        }

        if(newline == NEWLINE_ON) {
            // Append a new line character as original string contained one
            line[++end] = '\n';
        }

        printf("%s", line);
    }

    printf("\nRemoved %d trailing whitespace(s)\n", count);
    return 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;
}