Trying to understand this code and the getchar function - c

Question

I'm trying to understand this code and I'm very confused:
I can't understand why is needed three time of the getchar function and I can't understand when the program is use that getchar functions.
The code is working very well and its took from here:
http://www.zetadev.com/svn/public/k&r/exercise.1-13.c
#include <stdio.h>
/* Exercise 1-13: Write a program to print a histogram of the lengths of words
in its input. It is easy to draw the histogram with the bars horizontal; a
vertical orientation is more challenging. */
/* At this point we haven't learned how to dynamically resize an array, and we
haven't learned how to buffer input, so that we could loop through it twice.
Therefore, I'm going to make an assumption that no word in the input will be
longer than 45 characters (per Wikipedia). */
#define MAX_WORD_LENGTH 45 /* maximum word length we will support */
main()
{
int i, j; /* counters */
int c; /* current character in input */
int length; /* length of the current word */
int lengths[MAX_WORD_LENGTH]; /* one for each possible histogram bar */
int overlong_words; /* number of words that were too long */
for (i = 0; i < MAX_WORD_LENGTH; ++i)
lengths[i] = 0;
overlong_words = 0;
while((c = getchar()) != EOF)
if (c == ' ' || c == '\t' || c == '\n')
while ((c = getchar()) && c == ' ' || c == '\t' || c == '\n')
;
else {
length = 1;
while ((c = getchar()) && c != ' ' && c != '\t' && c != '\n')
++length;
if (length < MAX_WORD_LENGTH)
++lengths[length];
else
++overlong_words;
}
printf("Histogram by Word Lengths\n");
printf("=========================\n");
for (i = 0; i < MAX_WORD_LENGTH; ++i) {
if (lengths[i] != 0) {
printf("%2d ", i);
for (j = 0; j < lengths[i]; ++j)
putchar('#');
putchar('\n');
}
}
}

Answer 1

This getchar() is used to make sure that when EOF is reached, the program
gets out of the while loop.
while((c = getchar()) != EOF)
This getchar is also in a while loop. It makes sure that the whitespace characters ' ', '\t', and '\n' are skipped.
while ((c = getchar()) && c == ' ' || c == '\t' || c == '\n')
;
To make the program more robust, the above line should really be:
while ((c = getchar()) != EOF && isspace(c))
This getchar is also in a while loop. It thinks that any character that is not a ' ', '\t', or '\n' is a word character and increments length for each such character.
while ((c = getchar()) && c != ' ' && c != '\t' && c != '\n')
++length;
Once again, to make the program more robust, the above line should really be:
while ((c = getchar()) != EOF && !isspace(c))

Answer 2

The function getchar() reads and returns a character from the standard input device.
Syntax is variable name = getchar(), variable can be of type int or char.
Here is the explanation for each getchar() call.
while((c = getchar()) != EOF)
This will check if you input EOF (i.e Ctrl+D in unix and Ctrl+Z in Windows system)
if (c == ' ' || c == '\t' || c == '\n')
while ((c = getchar()) && c == ' ' || c == '\t' || c == '\n');
This will check if you input space, tab and new line character if yes then skip those and return to while((c = getchar()) != EOF)
length = 1;
while ((c = getchar()) && c != ' ' && c != '\t' && c != '\n')
++length;
Anyother character other than space, tab and new line character will result in executing ++length.