C Programming Language 2nd edition exercise 1-12 question

Question

Why the below condition:

if (c !=' ' && c !='\t' && c !='\n')

matches either:

not space + not \n - when input is "abc \n"

or

not \t + not \n - when input is "abc\t\n"

When AND logical operator is used? Should not AND require to match all conditions the same time?

Not space + NOT \t + NOT \n

#include <stdio.h>

#define IN   1  /* inside a word */
#define OUT  0  /* outside a word */

int main() {
       int c, state;
       state = OUT;
       while ((c = getchar()) != EOF) {
           
           if (c !=' ' && c !='\t' && c !='\n')
           
           {
               printf("%c", c);
               state = IN;    
           }
           
           else if (state)
           
           {
               printf("\n");
               state = OUT;
           }
           
       }
}

Answer 1

You seem to be confused regarding what the condition is actually checking for.

This condition:

if (c !=' ' && c !='\t' && c !='\n')

Written out as English, says: "if c is not a space AND c is not a tab AND c is not a newline".

In other words, the condition is true when c matches none of those 3 characters.

Answer 2

It is working as intended, test it with vertical-tab.

#include <stdio.h>

#define IN   1  /* inside a word */
#define OUT  0  /* outside a word */

int main() {
    int c, state;
    state = OUT;
    while ( (c = getchar()) != EOF) {
        if (c != ' ' && c != '\t' && c != '\n') {
            printf ("%c", c);
            state = IN;
        } else if (state) {
            printf ("\v");
            state = OUT;
        }
    }
    return 0;
}

space, newline & tab chars are ignored and after every word we print a vertical-tab. We see this step pattern to prove that.

There are tabs in 2nd edition

./a.out 
C Programming Language 2nd          edition exercise 1-12 question
C
 Programming
            Language
                    2nd
                       edition
                              exercise
                                      1-12
                                          question