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 this he means input something like...

We(blank)(blank)(blank)go(blank)to(blank)(blank)(blank)the(blank)mall!

... and output it like:

We(blank)go(blank)to(blank)the(blank)mall!

This is probably easier than I'm making it out to be, but still, I can't seem to figure it out. I don't really want the code... more so pseudo code.

Also, how should I be looking at this? I'm pretty sure whatever program I write is going to need at least one variable, a while loop, a couple if statements, and will use both the getchar() and putchar() functions... but besides that I'm at a loss. I don't really have a programmers train of thought yet, so if you could give me some advice as to how I should be looking at "problems" in general that'd be awesome.

(And please don't bring up else, I haven't got that far in the book so right now that's out of my scope.)

Answer 1

#include <stdio.h>   
main()
{
    int CurrentChar, LastChar;
    LastChar = '1';
    while ((CurrentChar = getchar()) != EOF)
    {
        if (CurrentChar != ' ')
        {
            putchar(CurrentChar);
            LastChar = '1';
        }
        else
        {
            if (LastChar != ' ')
            {
                putchar(CurrentChar);               
                LastChar = ' ';
            }                   
        }   
    }
}

Answer 2

I am also starting out with the K&R textbook, and I came up with a solution that uses only the material which had been covered up until that point.

How it works:

First, set some counter 'blanks' to zero. This is used for counting blanks.

If a blank is found, increase the counter 'blanks' by one.

If a blank is not found, then first do a sub-test: is the counter 'blanks' equal or bigger than 1? If yes, then first, print a blank and after that, set the counter 'blanks' back to zero.

After this subtest is done, go back and putchar whatever character was not found to be a blank.

The idea is, before putcharing a non-blank character, first do a test to see, if some blank(s) were counted before. If there were blanks before, print a single blank first and then reset the counter of blanks. That way, the counter is zero again for the next round of blank(s). If the first character on the line is not a blank, the counter couldn't have increased, hence no blank is printed.

One warning, I haven't gone very far into the book, so I'm not familiar with the syntax yet, so it's possible that the {} braces might be written in different places, but my example is working fine.

#include <stdio.h>

/* Copy input to output, replacing each string of one or more blanks by a single blank. */

main()
{
    int c, blanks;

    blanks = 0;
    while ((c = getchar()) != EOF) {
        if (c != ' ') {
            if (blanks >= 1)
                printf(" ");
                blanks = 0;
            putchar(c); }
        if (c == ' ')
            ++blanks;
    }
}

Answer 3

Considering what's asked in the question, I have also made sure that the program runs smooth in case of various tabs, spaces as well as when they're clubbed together to form various combinations! Here's my code,

int c, flag = 1;
    printf("Enter the character!\n");
    while ((c = getchar()) != EOF) {
    if (c == ' '||c == '\t') {
        c=getchar();
        while(c == ' '|| c == '\t')
               {
                   c = getchar();
               }
        putchar(' ');
        if (c == EOF) break;
    }
    putchar(c);
}

Feel free to run all test cases using various combinations of spaces and tabs.

Answer 4

#include <stdio.h>
int main()
{
    int c;
    while( (c = getchar( )) != EOF )
    {           
        if (c == ' ') 
        {
            while ((c = getchar()) == ' ');
            putchar(' ');
            putchar(c);
        }
        else 
            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

#include <stdio.h>
main()
{
    int c, numBlank=0 ;
    while((c= getchar())!=EOF)
    {
        if(c ==' ')
    {
        numBlank ++;
        if(numBlank <2)
        {
        printf("character is:%c\n",c);
        }
    }
    else
    {
        printf("character is:%c\n",c);
        numBlank =0;
    }
    }
}