Basic strcat query from k&r book

I am trying to understand postfix & prefix increment and decrement operators from K&R book. They have given a string concatenation example:

Code:

---

/* strcat: concatenate t to end of s; s must be big enough */
void strcat(char s[], char t[])
{
int i, j;
i = j = 0;
while (s[i] != '\0') /* find end of s */
i++;
while ((s[i++] = t[j++]) != '\0') /* copy t */
;
}

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I've used the above function in my code but to mess around (and to understand concept) I've switched the opertors:

Code:

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#include <stdio.h>
#include <stdlib.h>
#define MAXLINE 50

void trcat (char source[], char target[]);


int main(void) {
        char target[MAXLINE] = "test";
        char source[MAXLINE] = "this is ";
        trcat(source, target);
        printf("%s", source);
}

void trcat(char s[], char t[])
{
int i, j;
i = j = 0;
while (s[i] != '\0') /* find end of s */
i++;
while ((s[++i] = t[++j]) != '\0') /* copy t */
;
}

---

Obviously I am not getting desired output but I am unable to pinpoint the problem.
In the above example concatenation starts to happen when i=8 but to mess around (++i) I prefix the offset so in my case i becomes 9 before assignment. Same is the case with j. So as per my understanding & at best program should have skipped a few characters but in my case the concatenation is not happening.
i.e. the output is just:

Quote:

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this is

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I am confused. Kindly help.

You're leaving the original '\0' in place and concatenating after it. So when you go to print a string, how does it determine when to stop printing characters? I.e. where the end of the string is.

Quote:

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Originally Posted by Tclausex

You're leaving the original '\0' in place and concatenating after it. So when you go to print a string, how does it determine when to stop printing characters? I.e. where the end of the string is.

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Thanks! So you saying (in other words) while that concatenation is happening it's not getting printed because of '\0'?

The printing will stop at the null terminator.

Example

Code:

---

#include <stdio.h>

int main(void)
{
        char* s = "sam\0aras";
        printf("%s\n", s);
        return 0;
}

---

Well, it's quite a simple concept to grasp. i++ is “yield the value of i, then add one to it and store it in i” and ++i is “add one to i, then yield that value and store it in i”. In your first snippet, after the second while statement, s[i] contains the '\0' character. When the second while statement is entered, s[i] is overwritten with the value of t[0]. This simply doesn't happen in your second snippet — the value of t[0] is stored in s[i + 1] instead, which is the character *after* the terminating '\0' in s.

@std10093 @Barney Now it does look quite obvious. Thanks for your help.