Thread: Entab - replacing blanks with tabs and blanks

Good evening. I have the following exercise from K&R:

Write a program entab that replaces strings of blanks with the minimum number of tabs and blanks to achieve the same spacing. Use the same stops as for detab . When either a tab or a single blank would suffice to reach a tab stop, which should be given preference?

What can I do to fit the logic of numberOfBlanks, numberOfTabs and printBlanks inside the code? I mean, I tried to put it after the else but that didn't work. I got something like:

Sansa s t a r k

I thought I could get the sum of every occurrence of a white space and then print all blanks after a word.

Code:

#include <stdio.h> 

#define MAX_BUFFER 1024
#define SPACE ' ' 
#define TAB '\t' 

//  gets a line
int getLine(char s[], int lim);

// calculates the number of spaces for a tab (a tab = 5 blanks)
int calculateNumberOfSpaces(int offset, int tabSize);

// calculates only the number of blanks
int numberOfBlanks(int whitespaces, int tabSize);

// calculates only the number of tabs
int numberOfTabs(int whitespaces, int tabSize);

// prints the amount of number of blanks and tabs
void printBlanks(int numberofblanks, int numberoftabs);

void printBlanks(int numberofblanks, int numberoftabs) 
{ 
  int i; 
  for(i = 0; i < numberoftabs; i++) 
  { 
    putchar('\t');  
  }
  for(i = 0; i < numberofblanks; i++) 
  { 
    putchar(' ');  
  }                  
}      

int numberOfBlanks(int whitespaces, int tabSize) 
{ 
   return whitespaces % tabSize;
}     

int numberOfTabs(int whitespaces, int tabSize) 
{ 
   return whitespaces/tabSize;
}     

int calculateNumberOfSpaces(int offset, int tabSize)
{ 
   return tabSize - (offset % tabSize);    
}          

int getLine(char s[], int lim) 
{ 
   int c, i; 
   for(i = 0; i < lim - 1 && (c = getchar()) != EOF && c != '\n'; i++) 
   { 
      s[i] = c;
   }
   if(c == '\n') 
   { 
     s[i] = c;
     ++i;   
   }        
   s[i] = '\0';                     
   return i;
}

int main() 
{ 
   /* 
    nw - number of white spaces
    tabSize - amount of white spaces for tab
    l - number of characters input
    j - number of spaces for tab
    nb - number of blanks only
    nt - number of tabs only

   */
   int i, nw, tabSize, l, j, k, nb, nt; 
   nt = nb = j = nw = i = 0;
   tabSize = 5;
   char buffer[MAX_BUFFER];
   
   while(getLine(buffer, MAX_BUFFER) > 0) 
   { 
     for(i = 0, l = 0; buffer[i] != '\0'; i++) 
     { 
        if(buffer[i] == TAB) 
        { 
          j = calculateNumberOfSpaces(l, tabSize);    
          nw += j;
          
          for(k = 0; k < j; k++) 
          { 
            l++;      
          }
        }
        else if(buffer[i] == SPACE) 
        { 
           ++nw;
           l++;
        }
        else { 
          putchar(buffer[i]);
          l++;    
        }
        /*
        I don't know how to fit these functions
        
        nb = numberOfBlanks(nw, tabSize);  
        nt = numberOfTabs(nw, tabSize);
        printBlanks(nb, nt);                             
        */
     }              
   }           
   return 0;     
}

Don't know how this post got missed, sorry for the delayed reply:

Is this supposed to only "entab" at the beginning of a line, or in the middle too?

If at the beginning only, the logic is pretty simple. For each line you read:
1. Calculate the number of "spaces" before the first non-space, i.e. the column number the first non-space char would appear in.
2. Calculate the number of tabs (spaces / tabsize) and the leftover spaces (spaces % tabsize) required to retab/entab it.
3. Using loops, print that many tabs followed by that many ("leftover") spaces.
4. Print the rest of the line.

Also, I might move that if-else logic from main into calculateNumberOfSpaces.

If you have to deal with this in the middle of a line too, it's a bit more complicated. I'm not totally clear on what the behavior should be, so I can't really help you.

On a side note:

Code:

    /* 
    nw - number of white spaces
    tabSize - amount of white spaces for tab
    l - number of characters input
    j - number of spaces for tab
    nb - number of blanks only
    nt - number of tabs only
 
   */

If you need a comment block like this, it means your variable names suck. They should have clear, concise, descriptive names. How about numWhitespaces, inputLen, numSpaces, numBlanks, numTabs? Then your code makes sense when you read it and you don't need to keep looking back at the comment block to figure out wtf you were using l for. The usage of a variable is clear every time you type/read it. And l (lower case ell) in particular is a horrible variable name. It often looks very similar or identical to a 1 (one) and I (upper case I).

No problem if the reply took some time. Thank you anyways. I will take a closer look at the variables from now on. The main thing is to make "entabs" between the words and because of this, I got lost. There is another program, from users.powernet.co.uk that I'll analyse. Many thanks.