C program with fully justification of text from file - c

Question

Here is my problem statement:
I have a small question related to a portion of code which I can't find a proper solution to. Again I'm not necessarily asking for a full solution I just hit a deadend. I need to read from a file lines (Don't know their lengths) find the maximum length of a line and add spaces between words on each line, evenly, so that they are fully justified (all lines have the same size as the max one).
Here is my code so far:
#include <stdio.h>
#include <stdlib.h>
int main() {
FILE *f;
char *word;
int j, i, m, n, c, k, z;
char aux[255] = "", aux1[255];
i = 0;
j = 0;
char file[100][100];
char s[100];
f = fopen("user_input.txt", "r");
m = 0;
while (fgets(file[i], sizeof(file[i]), f)) {
if (m < strlen(file[i]) - 1)
m = strlen(file[i]) - 1;
i++;
}
for (j = 0; j < i; j++) {
n = 0;
for (k = 0; k < strlen(file[j]); k++)
if (file[j][k] == ' ')
n++;
c = (m - strlen(file[j])) / n;
for (z = 0; z < c; z++)
aux[z] = ' ';
for (k = 0; k < strlen(file[j]); k++)
if (file[j][k] == ' ') {
strcpy(aux1, file[j] + k + 1);
strcat(file[j], aux);
strcat(file[j], aux1);
}
printf("%s", file[j]);
}
}

Answer 1

Your code is broken for multiple reasons:
you forgot to include <string.h>
you have hard coded limits to the maximum line length and the number of lines, both causing a penalty of 0.5p
you do not test for fopen() success, causing undefined behavior upon failure to open the file.
you do not test array boundaries when reading lines, causing undefined behavior if the file has more than 100 lines or 99 byte fragments thereof.
your computation of c = (m - strlen(file[j])) / n; is rounded down. You will not insert enough spaces for full text justification in many cases.
aux is not properly null terminated, it will keep growing up to the largest number of spaces to insert for any given line.
the insertion operation will corrupt the line and ultimately leave just the last word with some spaces inserted before.
the code was badly formated and since you do not use {} for non trivial statement, it is difficult to read and easy to break.
Here is a modified version that does not have such limitations:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
const char *filename = "user_input.txt";
FILE *f;
char *line;
int c, i, len, maxlen, skip, nw, spaces, ns;
/* open the file */
if ((f = fopen(filename, "r")) == NULL) {
fprintf(stderr, "cannot open %s\n", filename);
return 1;
}
/* first pass: determine the maximum line length */
for (maxlen = len = 0;;) {
c = getc(f);
if (c == '\n' || c == EOF) {
if (maxlen < len)
maxlen = len;
len = 0;
if (c == EOF)
break;
} else {
len++;
}
}
/* allocate the line buffer: maxlen characters plus newline plus '\0' */
if ((line = malloc(maxlen + 2)) == NULL) {
fprintf(stderr, "cannot allocate memory for %d bytes\n", maxlen + 2);
fclose(f);
return 1;
}
/* second pass: read one line at a time */
rewind(f);
while (fgets(line, maxlen + 2, f)) {
len = strlen(line);
if (len > 0 && line[len - 1] == '\n') {
/* strip the newline if any */
line[--len] = '\0';
}
/* skip and output initial spaces */
for (skip = 0; line[skip] == ' '; skip++) {
putchar(line[skip]);
}
/* count the words */
for (nw = 0, i = skip; i < len; i++) {
if (line[i] == ' ')
nw++;
}
/* output the text, expanding spaces */
spaces = maxlen - len;
for (i = skip; i < len; i++) {
if (line[i] == ' ') {
ns = spaces / nw;
printf("%*s", ns, "");
spaces -= ns;
nw--;
}
putchar(line[i]);
}
putchar('\n');
}
free(line);
fclose(f);
return 0;
}