CODEWITHSUNDEEP
cpointerschar
Ian
Ian

Reputation: 695

Problems with C pointers

So I've been having trouble just understanding pointers in C. My problem is how to make char * find_ch_ptr return a char*. I've also been getting cast problems all over the place. If there is something wrong in here, can you please explain it fully?

/*
 * Return a pointer to the first occurrence of <ch> in <string>,
 * or NULL if the <ch> is not in <string>.
 *****
 * YOU MAY *NOT* USE INTEGERS OR ARRAY INDEXING.
 *****
 */
char *find_ch_ptr(char *string, char ch) {
        char * point = (char*)(string + 0);
        char * c = &ch;
        while(point != '\0') {
                if(point == c) return (char*)point;
                else *point++;
        }
        return (char*)point;    // placeholder
}

Upvotes: 1

Views: 291

Answers (5)

user3192104
user3192104

Reputation: 21

The while loop condition needed to be dereferenced before checking equivalence '\0'.

There is no need for the c variable, you can use the ch parameter directly for the check inside the while loop.

Here is a working example:

#include<stdio.h>

char *find_ch_ptr(char *string, char ch) {
    char *point = string;
    while(*point != '\0') {
            if(*point == ch)
            {
                    return point;
            }
            else
            {
                    point++;
            }
    }
    return point;    // placeholder
}

int main(int argc, char* argv[]){
    printf("%c\n", *find_ch_ptr("hello world", 'r'));
    return 0;
}

Upvotes: 2

pm100
pm100

Reputation: 50210

heres a working version of your code

Please tell you teacher that you got it from stack overflow

char *find_ch_ptr(char *string, char ch) {

        while(*string != '\0') {
                if(*string == ch) 
                   return string;
                else string++;
        }
        return (char*)0;
}

or the K&R way

while(*string && *string!=ch);
return str;

Upvotes: 2

Gopi
Gopi

Reputation: 19874

while(point != '\0')

should be

while(*point != '\0')

There are places where you need to dereference the pointer and you are not doing it.Like

while(*point != '\0')
{
  if(*point == ch)
  return point;
  else
  point ++;
}

PS: point is a pointer pointing to some valid memory location and the value stored in that location is got by dereferencing it *point

Upvotes: 5

Hugues Paquet Blanchette
Hugues Paquet Blanchette

Reputation: 612

Try something like strchr()

Usage:

#include <string.h>
ptr = strchr( s, c );

Upvotes: 2

Iharob Al Asimi
Iharob Al Asimi

Reputation: 53026

To compare the character currently pointed to by point you need to dereference point with the * operator like this

while (*point != '\0')

Then you want to compare the character that you are searching for but you are doing it the wrong way too.

You are comparing the address of the variable ch to the address currently point points to, that is wrong you need

if (*point == ch)

instead.

Upvotes: 2

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