C programming language excercise1-18 - c

Question

Hi guys i am reading The C programming language by Kernighan and Ritchie and trying to solve along the questions. This program is supposed to eliminate all the blanks and tabs from the end of the input lines but its not working.
I have added comments to the section of code i am having problems with
#include <stdio.h>
#define MAXLINE 1000
int getline(char line[], int max);
void copy(char to[], char frm[]);
int main(void) {
int maxLen=0;
int currLen;
char line[MAXLINE];
char longestLine[MAXLINE];
while((currLen=getline(line,MAXLINE)) > 0){
if(currLen > maxLen){
maxLen = currLen;
copy(longestLine, line);
}
}
if(maxLen>0){
printf("%d\n", maxLen);
printf("%s", longestLine);
}
return 0;
}
int getline(char line[], int max){
int c,i;
for(i=0;i<max-1 && (c=getchar())!=EOF && c!='\n';i++){
line[i] = c;
}
if(c == '\n'){
/* This is the logic i added to take care of the trailing
spaces and tabs. Rest of the program is same as the book
Its still counting spaces at the end of line when variable maxLen is
printed in the main function, would like to know if the logic is
erronous*/
while(line[i] == ' ' || line[i] == '\t'){
i--;
}
line[i]=c;
++i;
}
line[i] = '\0';
return i;
}
void copy(char to[], char from[]){
int i=0;
while((to[i]=from[i])!='\0'){
++i;
}
}

Answer 1

As far as i can tell, your program is returning the longest line entered, and does not eliminate blanks or tabs.
you are welcome to see the solution the link below:
solution to 1-18
I hope this helped
good luck

Answer 2

First, let's take a look at your output:
if(maxLen>0){
printf("%d\n", maxLen);
printf("%s", longestLine);
}
This part isn't in any loop and does not contain any loop, so it prints just one line. However, the program should print all the lines. Therefore, your code that prints lines should be in a loop similar to the code that gets a line. They could be in the same loop, like this:
while there is text left
get line
removing the spaces
print line
end loop
Or in different loops. Actually, I think you misunderstood the exercise, because it's printing the longest one, and that cleary seems to be your intention going by your code.
Deleting the whitespace
It seems that this is where you're trying to delete the whitespace:
while(line[i] == ' ' || line[i] == '\t'){
i--;
}
Note that the i you're using here is not the i from this line:
for(i=0;i<max-1 && (c=getchar())!=EOF && c!='\n';i++){
Instead, it's the i from this line:
int c,i;
This is because in for(i=0; ... you're defining another i so that one is in scope for the loop. The first i isn't touched in that loop and is still uninitialized when you try to delete the whitespace. So line[i] is undefined behavior and will most likely just crash your program. And even if it doesn't, it will just read a rubbish value, see if it coincidentally translates to ' ' or '\t' and then either not do anything, or decrease i and try again.
My suggestion to you is that you should try to solve the exercise incrementally. The task can be split in multiple parts:
Removing trailing whitespace from a line
Reading in the input
Do one after another. First, you write a program that takes one hardcoded line and removes the trailing whitespace and prints it. Then, when that works, you modify it to work with not one line, but with all the input lines. This way you don't have multiple parts that aren't working, but instead you can focus on doing one part at a time. It's easier to write software this way.

Answer 3

Thanks for your help guys. Problem was with the value of i in function getLine. Here is the solution:
int getline(char line[], int max){
int c,i;
for(i=0;i<max-1 && (c=getchar())!=EOF && c!='\n';i++){
line[i] = c;
}
i--; /* This line is the fix, value of i is incremented before termination of the
loop, so decrement it to point to the last character in the array */
while(line[i] == ' ' || line[i] == '\b'){
i--;
}
if(c == '\n'){
line[i]=c;
++i;
}
line[i] = '\0';
return i;
}