Why isn't my coding reading the \n - c

Question

I was writing a code that takes a sentence and reverses it, as an exercise. Here's what I wrote:
#include <stdio.h>
int main(void)
{
char a, sentence[100], sign;
char *c = sentence;
printf("Enter a sentence: ");
while ( (a = getchar()) != '\n' )
{
if ( a == '?' || a == '!' || a == '.')
{
sign = a;
break;
}
*c = a;
c++;
}
for (char *d = c; d >= sentence; d--)
{
if ( (d == sentence) && (*d != ' ') )
{
for (char *a = d; a < d + 99; a++)
{
if ( (*a == ' ') || (*a == '\n')) //code isn't reading the \n
{
break;
}
else
printf("%c", *a);
}
}
if ( (*d == ' ') && (d != c) && (d != sentence + 99) )
{
for (char *a = d+1; a <= c; a++)
{
if ( (*a == ' ') || (a == c))
{
printf(" ");
break;
}
else
printf("%c", *a);
}
}
}
printf("%c\n", sign);
return 0;
}
It works fine when I input a sentence with spaces in it:
Enter a sentence: This is a sentence
sentence a is This
However if I input a string with no spaces, like this:
Enter a sentence: Thisisasentence
I get an output with what was originally entered ('Thisisasentence'), followed by a lot of gibberish output. From what I understand, this is because the code doesn't go into the if ( (*a == ' ') || (*a == '\n') condition.
Why isn't the compiler reading the '\n'

Answer 1

The program works with a couple of changes.
In the while add *c = '\0'; after c++; to terminate the string.
Check for a == '\0' instead of '\n' as the while excludes the '\n'.
Added a check at the end of the while to make sure no more than 99 characters are allowed.
#include <stdio.h>
int main(void)
{
char a, sentence[100], sign;
char *c = sentence;
printf("Enter a sentence: ");
while ( (a = getchar()) != '\n' )
{
if ( a == '?' || a == '!' || a == '.')
{
sign = a;
break;
}
*c = a;
c++;
*c = '\0';//terminate
if ( c - sentence >= 99) {//make sure not too many characters
break;
}
}
for (char *d = c; d >= sentence; d--)//start at c and work back to sentence[0]
{
if ( (d == sentence) && (*d != ' ') )
{
for (char *a = d; !( *a == ' ' || *a == '\0'); a++)
{
printf("%c", *a);
}
}
if ( (*d == ' ') && (d != c) && (d != sentence + 99) )
{
for (char *a = d+1; a <= c; a++)
{
if ( (*a == ' ') || (a == c))
{
printf(" ");
break;
}
else
printf("%c", *a);
}
}
}
printf("%c\n", sign);
return 0;
}

Answer 2

It is probably best to split to work into two functions, one for reading a line of text and one for reversing it:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
void reverse_string(char *str) {
/* skip null */
if (str == 0) {
return;
}
/* skip empty string */
if (*str == 0) {
return;
}
/* get range */
char *start = str;
char *end = start + strlen(str) - 1; /* -1 for \0 */
char temp;
/* reverse */
while (end > start) {
/* swap */
temp = *start;
*start = *end;
*end = temp;
/* move */
++start;
--end;
}
}
char *read(void) {
char *line = malloc(100), *linep = line;
size_t lenmax = 100, len = lenmax;
int c;
if (line == NULL)
return NULL;
for (;;) {
c = fgetc(stdin);
if (c == EOF)
break;
if (--len == 0) {
len = lenmax;
char *linen = realloc(linep, lenmax *= 2);
if (linen == NULL) {
free(linep);
return NULL;
}
line = linen + (line - linep);
linep = linen;
}
if ((*line++ = c) == '\n')
break;
}
*line = '\0';
return linep;
}
int main(void) {
printf("Enter a sentence:");
char *sentence = read();
reverse_string(sentence);
printf(sentence);
return 0;
}
Test 1
Enter a sentence:this is a sentence
ecnetnes a si siht
Test 2
Enter a sentence:thisisasentence
ecnetnesasisiht