maximum line length program prints unreadable characters in c - c

Question

I am trying to run the maximum line length program as shown in chapter one of "The c programming language" and the output is always a series of question mark boxes like ⍰.
Here is the code:
#include <stdio.h>
#define MAXLINE 1000 /* maximum input line size */
int getline(char line[], int maxline);
void copy(char to[], char from[]);
/* print longest input line */
int main()
{
int len; /* current line length */
int max; /* maximum length seen so far */
char line[MAXLINE]; /* current input line */
char longest[MAXLINE]; /* longest line saved here */
max =0;
while((len = getline(line, MAXLINE)) > 0)
if (len > max) {
max = len;
copy(longest, line);
}
if (max > 0) /* there was a line */
printf("%s", longest);
return 0;
}
/* getline: read a line into s, return length */
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;
}
/* copy: copy 'from' into 'to'; assume to is big enough */
void copy(char to[], char from[])
{
int i;
i = 0;
while ((to[i] = from[i]) != '\0')
++i;
}
Is this a technical issue or something obviously wrong with the code?
Thank-you?

Answer 1

You have a tiny, tiny typo. This line in the getline function:
for (i = 0; i < lim - 1 && (c = getchar() != EOF) && c != '\n'; ++i)
should be
for (i = 0; i < lim - 1 && (c = getchar()) != EOF && c != '\n'; ++i)
The effect of this typo is that you call getchar(), test the returned value to see if it's equal to EOF or not, and assign the 1/0 (true/false) value to the variable c. But what you want to do is assign the returned value from getchar() to c, and then test to see if it's equal to EOF.
So if you type, say, "test", your typo-afflicted getline function was not writing the characters t e s t into line; instead it was writing four 1 values (that is, the character '\001', which is a control-A if you want to think about it that way), and since that's not a printing character, your display system printed it as a little box instead.