'SER_' or '_' character appearing in end of (string)output in c - arrays

Question

I am trying to print each word in a single line of a given sentence. It worked perfectly fine but a '_' appears in end of line. please help me with it and also proper manar to write it.
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
int main() {
char *s,i,check=0;
s = malloc(1024 * sizeof(char));
scanf("%[^\n]", s);
s = realloc(s, strlen(s) + 1);
for(i=0;i<1024;i++ ||check<=2)
{
if(*(s+i)!=' ')
{
printf("%c",*(s+i));
check=0;
}
else
{
printf("\n");
check++;
}
// fflush(stdin);
}
return 0;
}
Output:
dkf fja fjlak d
dkf
fja
fjlak
d SER_
Output2:
-for(i=0;i<20;i++ ||check<=2)-
hello I am suraj Ghimire
hello
I
am
suraj
Ghi

Answer 1

I am not sure your code works as you say..
The type of i is not a char *, so it should be int.
You process the input string without considering the NULL terminating char, which leads to a lot of garbage prints.
You do not release allocated memory.
I suggest this slightly modified version:
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
int main() {
char *s, *p;
/* Allocate a new string and verify the allocation has succeeded. */
s = malloc(1024 * sizeof(char));
if (!s) {
printf("malloc failed\n");
return 1;
}
/* Read from user. */
scanf("%[^\n]", s);
/* Work on a copy of `s` (must simpler and faster than a indexed access). */
p = s;
while (*p) {
if (*p != ' ') {
printf("%c",*p);
}else{
printf("\n");
}
p++;
}
free(s);
return 0;
}
Example output:
$ ./a.out
abc def gh i j kmlm opqrst
abc
def
gh
i
j
kmlm
opqrst
EDIT: As requested by the OP, further details regarding the NULL terminating char.
By convention, strings (array of characters) end with a specific character which we call the NULL terminating char. This character is 0 and marks the end of the string data.
In your example, the buffer which store the string is dynamically allocated in RAM. If you do not check for the NULL terminating character of the string, then you keep processing data as if it is part of the string (but it is not).
Going beyond this character make you access the following memory data (which is part of your program RAM data). Since these data can be anything (ranging from 0 to 255), printing them may lead to "gibberish" because they may not be printable and are definitely not consistent with your string.
In the "best" case the program halts with a "segmentation fault" because you are accessing a memory region you are not allowed to. In the "worst" case you print a lot of things before crashing.
This is typically called a data leak (whether it is RAM or ROM) because it exposes internal data of your program. In the specific case of your example there no sensitive data. But! Imagine you leak passwords or private keys stored in your program .. this can be a severe security issue!

Answer 2

There are a couple issues with your code.
Firstly, you need to check that the for loop does not exceed the bounds of the string.
Your for loop is always set to true because the logical OR operator || has a higher precedence than the comma operator. Because of this the loop will always run unless it gets stopped with break
Lastly your check is never reset to 0 after it reaches a value of 2.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main() {
char *s,i,check=0;
s = malloc(1024 * sizeof(char));
scanf("%[^\n]", s);
s = realloc(s, strlen(s) + 1);
for(i=0; i<strlen(s); i++) {
if(*(s+i) != ' ') {
printf("%c",*(s+i));
check=0;
} else {
printf("\n");
check++;
if (check > 2) break;
}
}
return 0;
}
Output:
Hello, this is a test
Hello,
this
is
a
test

Answer 3

for(i=0;i<1024;i++ ||check<=2)
There are two issues. One is length of string won't always be 1024, so it might be good to determine the length of string before print the string. The other is check<=2, which have to put in the second part of the for loop, so the test will be evaluated. Also it is better to calculate the length of string once. So I store the length of string in len.
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
char *s, i, check = 0;
s = malloc(1024 * sizeof(char));
scanf("%[^\n]", s);
s = realloc(s, strlen(s) + 1);
size_t len = strlen(s);
for (i = 0; i < len || check <= 2; i++) {
if (*(s + i) != ' ') {
printf("%c", *(s + i));
check = 0;
} else {
printf("\n");
check++;
}
// fflush(stdin);
}
return 0;
}