how to determine last words of each string? - c

Question

I have this assignment:
Enter a sequence of sentences from the keyboard into the string array (the end of entering - empty string). Determine the last word of each of these sentences.
The problem is that my program outputs the last word of the last sentence, and I need the last word of each sentence to be output.
Program I have tried:
#include <stdio.h>
#include <string.h>
int main() {
char str[10][100];
int i;
printf("Enter a sequence of sentences:\n");
for (i = 0; i < 10; i++) {
if (*gets(str) == '\0')
break;
}
printf("The last word of each of these sentences is:\n");
for (i = 0; i < 10; i++) {
char *word;
word = strtok(str[i], ".");
while (word != NULL) {
char *last_word = word;
word = strtok(NULL, ".");
}
printf("%s\n", last_word);
}
return 0;
}

Answer 1

The delimiter in this call
word = strtok(str[i], ".");
does not make sense.
It seems you mean
word = strtok(str[i], " \t.");
provided that a sentence can be ended only with a dot and words are separated by spaces or tab characters.
Another problem is that the variable last_word must be declared before the while loop.
For example
char *last_word = NULL;
char *word;
word = strtok(str[i], " \t.");
while (word != NULL) {
last_word = word;
word = strtok(NULL, " \t.");
}
And it is better to use for loop instead of the while loop
char *last_word = NULL;
for ( char *word = strtok(str[i], " \t." );
word != NULL;
word = strtok(NULL, " \t.") )
{
last_word = word;
}
Pay attention to that the function gets is unsafe and is not supported by the C Standard. Instead use standard C function fgets.
And the condition in the second for loop
for(i=0; i<10; i++)
{
char *word;
//...
is incorrect because the user can enter less than 10 sentences.

Answer 2

Without repeating the commentary of the accepted answer provided by #Vlad (kudos!), here is an alternative offering (with comments)
#include <stdio.h>
#include <string.h>
int main( void ) {
// A single large buffer allowing very long lines to be entered.
char buf[ 10 * 100 ], *p = buf;
size_t left = sizeof buf;
int i = 0;
// up to 10 'lines' of input, breaking on an empty line, too
while( i++ < 10 && fgets( p, left, stdin ) && p[0] != '\n' ) {
// typical invocation of strtok() to isolate "words"
// and a "wasteful" copy of each word to the current start of the buffer
for( char *tkn = p; ( tkn = strtok( tkn, " .\n" ) ) != NULL; tkn = NULL )
strcpy( p, tkn );
// having copied the last "word", append '\n' and advance the pointer
size_t len = strlen( p );
p += len;
strcpy( p++, "\n" );
left -= len + 1; // eroding the available size of the buffer
}
printf( "%s", buf ); // a single output of "word1\nword2\nword3\n..."
return 0;
}
NB: strcpy() of overlapping buffers is fraught with hazards. This works in this case, but the practise and its effects must be very well considered before using this technique.