recursive function that return the first index where sub string contained in string

Question

I need to make a recursive function, that gets two char arrays, and return the first index where "subStr" appear in the "str".

Signature of the function:

int strIndex(char str[], subStr[]);

For example- for str="abcdebc" and subStr="bc", it will return 1(because 1 is the first index where subStr contained in str), and for str="ab" and subStr="ab" it will return 0. If subStr doesn't contained in str(for example str="abc", subStr="aa"), it will return -1.

This is what I tried to do:

int strIndex(char str[], char subStr[])
{
    if (strcmp(str, subStr) == 0)
        return 0;
    else if (strcmp(str + (strlen(str1) - strlen(subStr)), subStr) == 0)
        return strlen(str) - strlen(subStr);
    else
        //return without the last element of "str" array
}

but does it possible to call in recurstion without the lest element of array?

Post your implementation of the recursive function and explain how it is not working as you expect. — drescherjm, Jan 26 '16 at 20:57
This is very easy using `strstr()` and doing some basic pointer arithmetik. Try it yourself! I do not see where a recursion is sensible here. Are you sure that you understood the assignment right? — Ctx, Jan 26 '16 at 21:09
@jaldk try solving it with the very basics. Don't use string functions. Compare character by character and think bout how to check for a substring in a string yourself. If you have problems solving it, why don't you ask the one who gave you that test? — Flikk, Jan 26 '16 at 21:17

score 1 · Answer 1 · answered Jan 26 '16 at 21:35

The function can look the following way

#include <stdio.h>
#include <string.h>

int indexOf( const char *s1, const char *s2 )
{
    size_t n1 = strlen( s1 );
    size_t n2 = strlen( s2 );

    if ( n1 < n2 )
    {        
        return -1;
    }
    else if ( strncmp( s1, s2, n2 ) == 0 )
    {
        return 0;
    }
    else
    {
        int rtn = 1 + indexOf( s1 + 1, s2 );
        return rtn == 0 ? -1 : rtn;
    }
}    

int main( void )
{
    const char *s = "abcdebc";
    const char *t = "bc";

    printf( "Index of \"%s\" in \"%s\" is %d\n", t, s, indexOf( s, t ) );
}

The program output is

Index of "bc" in "abcdebc" is 1

recursive function that return the first index where sub string contained in string

1 Answers1