K&R 1.19 exercise ("reverse" func) - c

Question

Here is the task:
Write a function reverse(s) that reverses the character string s . Use it to write a program that reverses its input a line at a time.
Ok, now, my performing:
#include <stdio.h>
#define LIM 40
char line[LIM];
int c;
int reverse(char line[], int lim);
int len;
int main(void) {
while ((len = reverse(line, LIM)) > 0) {
;
}
printf("\n END OF THE PROGRAM \n");
return 0;
}
********** THE REVERSE FUNCTION*********
int reverse(char s[], int lim) {
char rev[LIM];
int 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';
int r;
for (r = 0; r < lim - 1; ++r) {
rev[r] = s[i];
--i;
}
int x;
for (x = 0; x < lim - 1; ++x) {
putchar(rev[x]);
}
printf("\n");
return r;
}
It seems to work correctly, but there are some bugs related to the output.
For example:
INPUT: hello everybody OUTPUT: ydobyreve olleh
INPUT: abc OUTPUT: cba'
INPUT: ABC OUTPUT: CBA'
INPUT: ABC ABC OUTPUT: CBA CBA
INPUT: se se OUTPUT: es es'
See? Some strange " ' " occurs in the end of output and I can't figure out any pattern why these "artifacts" get printed. It happens randomly (for me). Could you please suggest anything, what's wrong in the code?

Answer 1

Your reverse function has problems:
You should not store the newline into the s array as you do not want it to take part in the reverse operation.
You should stop the subsequent for loop when you reach the end of the string in s, not run all the way to the end of the buffer.
You should null terminate the rev array.
You do not need to output the rev array one character at a time, use is as a string.
Here is a corrected and simplified version:
#include <stdio.h>
#define LIM 40
int reverse(char line[], int size);
int main(void) {
char line[LIM];
int len;
while (reverse(line, LIM) > 0) {
continue;
}
printf("\n END OF THE PROGRAM \n");
return 0;
}
/* THE REVERSE FUNCTION */
int reverse(char s[], int size) {
char rev[size];
int i, r, c, len;
for (i = 0; i < size - 1 && (c = getchar()) != EOF && c != '\n'; i++) {
s[i] = c;
}
len = i;
s[i] = '\0';
for (i = 0; i < len; i++) {
rev[len - i - 1] = s[i];
}
rev[i] = '\0';
printf("%s\n", rev);
return len;
}

Answer 2

A bit more modular solution. I wasn't exactly sure what K&R meant by "one line at a time". But this will reverse the string until it finds a newline. Then wait for the user and repeat.
#include <stdio.h>
#define MAXLINE 1000
int get_line(char s[], int limit);
int reverse(char to[], char from[], int l);
int main() {
int size;
char line[MAXLINE];
while ((size = get_line(line, MAXLINE)) > 0) {
char revline[size];
int len = reverse(revline, line, size);
printf("%s\n", revline);
}
return 0;
}
int reverse(char to[], char from[], int l) {
int i;
int j = l - 2;
for (i = 0; i < l; i++, j--) {
to[i] = from[j];
}
to[i] = '\0';
return i;
}
// read a line into s until limit
// return length of line
int get_line(char s[], int limit) {
int c = 0;
int i = 0;
for (i = 0; i < limit-1 && (c = getchar()) != '\n'; ++i) {
s[i] = c;
}
if (c == '\n') {
s[i] = c;
++i;
}
s[i] = '\0';
return i;
}
Output:
testing one two
owt eno gnitset
three four
ruof eerht
five six
xis evif