String Search C program without using built-in functions - c

Question

I have a problem in my C program. This is the String Search program. The problem is when I type the String aabaaacaamaad, the result comes NULL when I search for ab in it but it should not as ab is there in aabaaacaamaad. The same result also comes with am and ad which is right but why does it come with aabaaacaamaad? Code:
char* MyStrstr(char* pszSearchString, char* pszSearchWord);
int main(int argc, char* argv[])
{
char szTemp1[20] = {0};
char szTemp2[10] = {0};
char * pszTemp1 = NULL;
strcpy(szTemp1, "aabaaacaamaad");
strcpy(szTemp2, "aa");
pszTemp1 = MyStrstr(szTemp1, szTemp2);
printf("%s", pszTemp1);
getch();
return 0;
}
char* MyStrstr(char* pszSearchString, char* pszSearchWord)
{
int nFcount = 0;
int nScount = 0;
int nSearchLen = 0;
int nIndex = 0;
char* pszDelString = NULL;
if(pszSearchString == NULL || pszSearchWord == NULL) {
return NULL;
}
while(pszSearchWord[nSearchLen] != '\0') {
nSearchLen++;
}
if(nSearchLen <= 0){
return pszSearchString;
}
for(nFcount = 0; pszSearchString[nFcount] != '\0'; nFcount++) {
if(pszSearchString[nFcount] == pszSearchWord[nScount]) {
nScount++;
} else {
nScount = 0;
}
if(nScount == nSearchLen) {
nIndex = (nFcount - nScount) + 1;
pszDelString = pszSearchString + nIndex;
return pszDelString;
}
}
return NULL;
}

Answer 1

I see what your code is trying to do, you want to avoid a loop in a loop but however you're missing one thing. When a match fails you're not going back but still moving forward in pszSearchString while you should not. The result of this flaw is that with incomplete matches you skip characters. That's the reason why the strstr function originally uses a loop in a loop so for every character in pszSearchString there is an new loop to match with pszSearchWord. Here the original strstr.c file from BSD/Darwin:
char * strstr(const char *in, const char *str)
{
char c;
size_t len;
c = *str++;
if (!c)
return (char *) in; // Trivial empty string case
len = strlen(str);
do {
char sc;
do {
sc = *in++;
if (!sc)
return (char *) 0;
} while (sc != c);
} while (strncmp(in, str, len) != 0);
return (char *) (in - 1);
}