findNword.c

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
#include <ctype.h>


// return a pointer to the first character that does not satisfy the function f
// or a pointer to the end of the string
char *skip(char *st, int (f)(char))
{
    assert(st != NULL);
    while (*st && f(*st))
        ++st;
    return st;
}

int is_word_char(char c)
{
    return isalnum(c);
}

int is_not_word_char(char c)
{
    return !is_word_char(c);
}

#define skip_punctuation(a) (skip(a, is_not_word_char))
#define skip_word(a) (skip(a, is_word_char))

char *find_n_word(char *sentence, int n)
{
    assert(sentence != NULL);
    assert(n >= 0);

    char *begin = skip_punctuation(sentence);

    for ( ; n > 0 && *begin != 0; n--) {
        assert(is_word_char(*begin));
        begin = skip_word(begin);
        begin = skip_punctuation(begin);
    }
    return *begin ? begin : NULL;
}


// removes the first word in sentence
// and returns it
char *remove_word(char *sentence)
{
    assert(sentence != NULL);


    if (*sentence == 0)
        return NULL;

    char *begin = sentence;

    // at this point there is at least one alpha
    assert(is_word_char(*begin));

    char *end = skip_word(sentence+1);
    assert(end > begin);

    char *word = strndup(begin, end - begin);
    assert(word != NULL);

    //shift memory, to the end
    memmove(begin, end, strlen(end)+1);
    

    return word;
}

int main(int iargs, char* args[])
{

    // read sentence from first parameter, number to remove from second

    if (iargs != 3) {
        fprintf(stderr, "Error: illegal number of parameters [%d]\n\nUsage: %s <sentence> <index-base 0>\n", iargs, args[0]);
        exit(1);
    }
    char *original = args[1];
    char *sentence = strdup(original);

    assert(sentence != NULL);

    int n = atoi(args[2]);
 
   if (n < 0) {
        fprintf(stderr, "Error: number of word should be a positive number [%d]\n\nUsage: %s <sentence> <index-base 0>\n", n, args[0]);
        exit(1);
    }

    char *index = find_n_word(sentence, n);
    if (index == NULL) {
        printf("Sentence %s does not contain a word at position %d\n", sentence, n);
        exit(1);
    }

    char *word =  remove_word(index);

    printf("Original sentence %s\nWithout %d word [%s]\nword [%s]\n", original, n, sentence, word);

    sentence = realloc(sentence, strlen(sentence)+1);
    assert(sentence != NULL);

    free(word);
    free(sentence);


    return 0;
}