Thread: How do pointers work

I've started to learn pointers, but I am not sure how pointer's operations work. Can you demonstrate on this piece of code how can I use pointers in practice
Thanx in advance!

Code:

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


void main()
{
int i;
int z;
int b = 0;
char ch[250];


printf("%s\n", " Enter line not longer than 250 characters");
gets_s(ch);



for (i=0; i<10; i++)
{
if  (i>4)
{
z = i;
b++;
break;
}
}
printf("%d%c", b, ch[z]);
}

What I have done so far, I've tried to use pointers with the same code, get no errors, but the program suddenly feezes in the execution process

Code:

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


void main()

{
    int i;
    int *i2;
    i2 = &i;

    int z;
    int *z2;
    z2 = &z;



    int b = 0;
    int *b2;
    b2 = &b;




    char ch[250];
    //char *ch2;
    //ch2 = &ch;


    printf("%s\n", " Enter line not longer than 250 characters");
    gets_s(ch);



    for (*i2 = 0; *i2<10; i2++)
    {
        if (*i2>4)
        {
            *z2 = *i2;
            *b2++;
                break;
        }
    }
    printf("%d%c", *b2, ch[*z2]);
}

Well first of all, main returns int, not void (despite what your compiler will let you get away with)
FAQ > main() / void main() / int main() / int main(void) / int main(int argc, char *argv[]) - Cprogramming.com

Second, gets_s is only "safe" if you read the manual and make a note of the fact that it takes TWO parameters.
https://msdn.microsoft.com/en-us/library/5b5x9wc7.aspx
You should be getting a warning about this.

If you're trying to run code with warnings, then it's a behaviour you really need to STOP doing NOW.

> for (i2 = 0; i2<10; i2++)
As an example, this would be
for (*i2 = 0; *i2<10; (*i2)++)

Well, ask yourself this.

What is ch[5] equal to? You are breaking out of the for loop once i2==5

What input are you using for your test case?

Well you're still calling gets_s wrong for starters.

After that, all bets are off.

Listen to what Salem has to say and then realize that your *b2 will not equal 6 the way you have your if statement set up right now.

A pointer is kind of like a variable, except that it POINTS to a real variable's location in memory. This is generally useful when you have a large data structure that is passed to a function. If pointers to the structure were not used, the structure will be created locally with each call of the function, which can cause your computer to run out of memory, depending on what your application is doing. Here is a small example:

Code:

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

struct dude {
    int i;
    int z;
    int b;
    char ch[250];
};
 
 
int main()
 
{
    dude *Pvar = new dude;

    printf("%s\n", " Enter line not longer than 250 characters");
    gets_s(Pvar->ch);
 
 
 
    for (Pvar->i = 0; Pvar->i<10; Pvar->i++)
    {
        if (Pvar->i>4)
        {
            Pvar->z = Pvar->i;
            Pvar->b++;
                break;
        }
    }
    printf("%d%c", Pvar->b, Pvar->ch[Pvar->z]);
}

By the way, I don't know what your code is trying to do, so my example works, but I don't know what it does.
Also, the 'new' operator is a c++ thing, because you were asking about pointers, and I do not know how to malloc memory..

c - What is gets() equivalent in C11? - Stack Overflow

Check this link. The first answer explains get_s.