K&R Exercise 1-9 (C)

Question

\"Write a program to copy its input to its output, replacing each string of one or more blanks by a single blank.\"

I\'m assuming by thi

Answer 1

Many others have already used the last character logic in their code, but perhaps the following version is easier to read:

int c, prevchar;
while ((c = getchar()) != EOF) {
    if (!(c == ' ' && prevchar == ' ')) {
        putchar(c);
        prevchar = c;
    }
}

Answer 2

I worked really hard at finding a solution that used only the material that has already been covered in the first part of the first chapter of the book. Here is my result:

#include <stdio.h>

/* Write a            program         to copy its input to       its output, replacing             each string of one         or more blanks by a single blank. */

main()
{
    int c;

    while ((c = getchar()) != EOF){
        if (c == ' '){
            putchar(c);
            while ((c = getchar()) == ' ')
                ;
        }
        if(c != ' ')
            putchar(c);
    }
}

Answer 3

#include <stdio.h>

main() {
    int input, last = EOF;
    while ((input = getchar()) != EOF) {
       if (input == ' ' && last == ' ') continue;
       last = input; 
       putchar(input);
    }
}

Answer 4

#include <stdio.h>
int main(void)
{
        long c;
        long nb = 0;
        while((c = getchar()) != EOF) {
                if(c == ' ' || c == '\t') {
                        ++nb;
                } else {
                        if(nb > 0) {
                                putchar(' ');
                                nb = 0;
                        }

                        putchar(c);
                }
        }
        return 0;
}

Answer 5

Look at your program as a machine that moves between different states as it iterates over the input.

It reads the input one character at a time. If it sees anything other than a blank, it just prints the character it sees. If it sees a blank, it shifts to a different state. In that state, it prints one blank, and then doesn't print blanks if it sees them. Then, it continues reading the input, but ignores all blanks it sees--until it hits a character that isn't a blank, at which point it shifts back to the first state.

(This concept is called a finite state machine, by the way, and a lot of theoretical computer science work has gone into what they can and can't do. Wikipedia can tell you more, though in perhaps more complicated detail than you're looking for. ;))

Answer 6

// K & R Exercise 1.9
// hoping to do this with as few lines as possible 

int c = 0, lastchar = 0;
c = getchar();
while (c != EOF) {
  if (lastchar != ' ' || c != ' ') putchar(c);
  lastchar=c;
  c=getchar();
}