Restarting while loop in c without integers - c

Question

I'm trying to get this code to work, but I have no idea how to restart the inner while loop. How would I do it?
/*
* Return a pointer to the first occurrence of any character in <stop>
* in the given <string> or NULL if the <string> contains no characters
* in <stop>.
*****
* YOU MAY *NOT* USE INTEGERS OR ARRAY INDEXING.
*****
*/
char *find_any_ptr(char *string, char* stop) {
char *newstring = (char*)0;
while(*stop != '\0'){
while(*string != '\0') {
if(*string == *stop){
if(newstring < string || newstring != (char*)0){
string++;
}else{
newstring = string;
string++;
}
}
}
stop++;
}
return newstring; // placeholder
}

Answer 1

Use a temporary variable for string pointer, and use this temp variable instead inside the inner loop.
while(*stop != '\0'){
char *p = string;
while (*p != '\0') {
... /* use 'p' in place of 'string' */
}
stop++;
}

Answer 2

This is relatively simple using nothing but a character pointer to the string and a pointer to stop. For each character in your string, you compare against each character in stop, returning the character in string on match, or NULL if no match is found:
#include <stdio.h>
char *find_any_index(char string[], char stop[]) {
char *p = string;
char *sp = NULL;
while (*p)
{
sp = stop;
while (*sp)
{
if (*sp == *p)
return p;
sp++;
}
p++;
}
return NULL;
}
int main (int argc, char **argv) {
if (argc < 3) {
printf ("usage: %s string stoplist\n", argv[0]);
}
printf ("\n string: %s\n stop : %s\n\n", argv[1], argv[2]);
printf (" first char in string matching a char in stop: %s\n\n", find_any_index (argv[1], argv[2]));
return 0;
}
Output
$ ./bin/find_substr_str thisIsAstring mase
string: thisIsAstring
stop : mase
first char in string matching a char in stop: sIsAstring

Answer 3

Here is a demonstrative program that shows how the function can be written
#include <stdio.h>
char * find_any_ptr( const char *string, const char* stop )
{
const char *p, *q;
_Bool found = 0;
p = string;
do
{
q = stop;
while ( *q && *q != *p ) ++q;
} while ( !( found = *q ) && *++p );
return ( char * )( found ? p : NULL );
}
int main(void)
{
const char *p = find_any_ptr( "abc9de", "1234567890" );
if ( p ) puts( p );
return 0;
}
The program output is
9de
Only I would name the function find_any_char instead of find_any_ptr:)

Answer 4

This is my implementation:
#include <stdio.h>
#include <stdlib.h>
char * findany(char *string, char *stop) {
char * app;
//To avoid segmentation fault!
if (stop==NULL || string==NULL || !*stop || !*string)
return NULL;
do {
app=string;
while(*app!=0 && *app!=*stop)
app++;
stop++;
} while(*app==0 && *stop!=0);
return (*app!=0)?app:NULL;
}
int main(void)
{
char string[100];
char stop[100];
char * found;
for(;;) {
printf("Insert a string without spaces[q<Enter> to exit]: ");
scanf("%s",string);
if (!strcmp(string,"q"))
break;
printf("Insert the chars to search without spaces: ");
scanf("%s",stop);
printf("Searching any occurence of a char in \"%s\""
" inside \"%s\"\n",stop,string);
found=findany(string,stop);
printf("%s\n",(found!=NULL)?found:"NULL");
}
return 0;
}
I think that is better to use also the following way to implement the function findany():
char * _findany(char *string, char *stop) {
char * app; // to start the first loop
//To avoid segmentation fault!
if (stop==NULL || string==NULL || !*stop || !*string)
return NULL;
do {
app=stop;
while(*app!=0 && *app!=*string)
app++;
string++;
} while(*app==0 && *string!=0);
return (*app!=0)?(string-1):NULL;
}
You may observe the difference between the two functions adding the function _findany in the code above and to call the new function adding the following code after (or before) the printf in the main above.
found=_findany(string,stop);
printf("%s\n",(found!=NULL)?found:"NULL");