K&R 1-19 // About adjusting the value of numerical counters - c

Question

This is a very peculiar doubt about an exercise form the K&R textbook, I don't have any idea what the "standard" answer is, so the program itself may be a bit unfamiliar.
I tried to describe in the code the incremental steps that brought this program together, my question is about an adjustment that by logic shouldn't have any impact but taking away a stray --i.
Instead, if I try it all kind of strange behaviours appear (I tried a few combinations so I won't go to the extent of desribing them all here.. )
#include <stdio.h>
#define MAXCHAR 15
int storeline(char line[], int lim);
void reverse(char in[], char out[], int len);
main() {
int l;
char line[MAXCHAR+2]; /*I add two position to accomodate a newline and a '\0' character */
char enil[MAXCHAR+2];
while ((l=storeline(line, MAXCHAR+2))>=0) {
if (l<MAXCHAR)
reverse(line, enil, l); /*reverse is called with the array (in this case a 17 characters array) and the count computed in storeline (up to )*/
else
reverse(line, enil, MAXCHAR);
printf("%s", enil);
}
return 0;
}
int storeline(char s[], int lim) {
int i;
int c;
for(i=0;i<lim-2&&(c=getchar())!='\n'&&c!=EOF;++i){ /* this loop breaks at i==15 */
if (c==' '||c=='\t') {
while((c=getchar())==' '||c=='\t');
s[i]=' ';
++i;
if(c==EOF)
break;
}
s[i]=c;
}
if (c!=EOF) {
s[i]='\n'; /* a newline is added in s[15] */
++i;
}
s[i]='\0'; /* a '\0' character is added at s[16] */
--i; /*no more characters have to be added so I bring the count of the characters down by 1 (a further unit is deducted by the fact that one character is stored in s[0] */
while (c!='\n' && c!= EOF) {
c=getchar();
i++;
}
return i; /* the count goes on and is subsequently returned by the function, newline is assumed to be a file break by design, but this is easily adjusted */
}
/* let's pretend the string was '123451234512345' and MAXCHAR is 15. */
void reverse (char in[], char out[], int len) {
int i, lim;
i=0;
lim=len-1; /*len was 15, now it is 14. note that the array goes up to in[16] */
while(lim>=0) {
out[i]=in[lim];
++i;
--lim;
}
out[i]='\n';
++i;
out[i]='\0';
}
My doubt is, if I remove the --i element in storeline and decrease lim to len-2 everything should work as before, but it doesn't/ Why? The numbers are literally the same..

Answer 1

I am not sure if I am getting it, but you are trying to mix up 1.18 and 1.19. By one side, you want to clean the input and, by the other, you are trying to reverse the line. I would suggest you divide what you want to do into different functions. It will not only make it easier to program but also will make it easier to detect errors. This way, I would make one function to get the line and store it into an array, exactly equal to the example given in the book. Then, I would do a second function to clean the lines and a third function which reversed the lines. However, if you want only to solve exercise 1.19, you only need to use the getline and reverse functions. I leave to you the part of writing the main() function.
This way, the getline function:
int getline(char line[], int maxsize)
{
int position, input_character;
input_character = 0;
for (position = 0; position < maxsize - 2 && (input_character = getchar()) != EOF && input_character != '\n'; ++position) {
line[position] = input_character;
}
if (input_character == '\n') {
line[position] = input_character;
++position;
}
line[position] = '\0';
return position;
}
The clean function:
void clean(char output[], char input[])
{
char storage[MAXLINE];
int output_character, storage_character, input_character;
output_character = 0;
storage_character = 0;
while (output[output_character] != '\0') { //This goes through output[] until it gets to the last written character
++output_character;
}
for (input_character = 0; input[input_character] != '\0' && output_character < (MAXCHAR * MAXLINE - 1); ++input_character) {
if (input[input_character] == ' ' || input[input_character] == '\t') {
storage[storage_character] = input[input_character]; //The array storage[] will store me the trailing blanks and tabs
++storage_character;
}
else if (input[input_character] == '\n') { //If there is a newline character and nothing has been copied into output, then it is a blank line and is not copied into output
if (output[output_character] == '\0') {
;
}
else {
output[output_character] = input[input_character]; //Copy the newline character
++output_character;
}
}
else {
storage[storage_character] = '\0';
for (storage_character = 0; storage[storage_character] != '\0'; ++storage_character) {
output[output_character] = storage[storage_character]; //If there is a character after blanks/tabs, copy storage into output
++output_character;
}
output[output_character] = input[input_character]; //Copy the character
++output_character;
storage_character = 0;
}
}
output[output_character] = '\0';
}
And the reverse function:
void reverse(char reversed[], char original[])
{
int size_original, output_char;
for (size_original = 0; original[size_original + 1] != '\n'; ++size_original) {
;
}
for (output_char = 0; size_original >= 0; ++output_char) {
reversed[output_char] = original[size_original];
--size_original;
}
reversed[output_char] = '\n';
reversed[output_char + 1] = '\0';
}
I hope this was useful. Feel free to comment if it didn't help and I will try to answer you.