C programming substring function help?

I'm assuming you don't want to use strstr from string.h, because searching for a substring is exactly what that function does.

You should really try to code this yourself; it's a good exercise that gives you a chance to work with pointers and puts your logic skills to the test. Give it a try, and compare what you have to what I did below. At the very least, study and understand my solution; I'm sure you can learn something doing that.

#include <stdio.h>

#include <string.h>

#define MAX_LINE_LEN 80

typedef enum { false = 0, true } bool;

char *getStr(const char *, char *, size_t);

char *substring(char *substring, char *string);

char s1[MAX_LINE_LEN];

char s2[MAX_LINE_LEN];

int main(int argc, char *argv[]) {

    char *p;

    while (1) {

        getStr("\nEnter string :",s1,MAX_LINE_LEN);

        getStr("Enter substring to find :",s2,MAX_LINE_LEN);

        if ((strlen(s1) > 0) && (strlen(s2) > 0)) {

            printf("%s is",s2);

            if ((p = substring(s2,s1)) == NULL) {

                printf(" not");

            }

            printf(" a substring of %s",s1);

            if (p != NULL) {

                printf(", found at index %d",p-s1);

            }

            printf("\n");

        }

    }

    return 0;

}

char *substring(char *substring, char *string) {

    char *p = NULL, *q = string, *z = substring;

    if ((z != NULL) && (q != NULL)) {

        while ((*q != '\0') && (*z != *q)) {

            q++;

        }

        if (*q != '\0') {

            p = q;

        }

        while ((*q != '\0') && (*z != '\0') && (*q == *z)) {

            q++; z++;

        }

        if (*z != '\0') p = NULL;

    }

    return p;

}

char *getStr(const char *prompt, char *str, size_t len) {

    char *p;

    printf("%s ",prompt);

    if ((p = fgets(str,len,stdin)) != NULL) {

        *(strchr(str,'\n')) = '\0';

    }

    return p;

}

#if 0

Sample run:

Enter string : abcd

Enter substring to find : ab

ab is a substring of abcd, found at index 0

Enter string : abcd

Enter substring to find : cde

cde is not a substring of abcd

Enter string : abcd

Enter substring to find : cd

cd is a substring of abcd, found at index 2

Enter string : abcd

Enter substring to find : d

d is a substring of abcd, found at index 3

Enter string : abcd

Enter substring to find : xyz

xyz is not a substring of abcd

Enter string : abc

Enter substring to find : bcde

bcde is not a substring of abc

#endif

can use strstr() functionality of <string.h> header document occasion: const char *largestring = "Foo Bar Baz"; const char *smallstring = "Bar"; char *ptr; ptr = strstr(largestring, smallstring); right here, ptr would have the index of the commencing incidence of smallstring in largestring. it is case soft. In case it isn't any longer present it is going to return null in case you do no longer decide for to apply the functionality then can write your man or woman code additionally; steps would be: a million. locate the dimensions of largestring and smallstring 2. run the outer loop from 0 until at last length-a million of largestring 3. start up matching the 1st character of smallstring with each character of the largestring. 4. everywhere the 1st experience happens, run a loop from a million to length-a million of smallstring 5. save checking each character of smallstring with characters of largestring from the place the experience became stumbled on 6. If everywhere the experience is fake set flag=fake and smash the internal loop else proceed 7. whilst the internal loop completes or breaks, verify flag. no rely if it is fake proceed the outer loop else print that' experience became stumbled on" and smash the outer loop additionally