difference between pen and *pen in this code [closed] - c

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int main(void)
{
char mine[5] = "hello";
char *pen = mine;
while(*pen != '\0')
{
printf("%c\n", *pen);
pen++;
}
}
int main(void)
{
char mine[5] = "hello";
char *pen = mine;
while(*pen != '\0')
{
printf("%c\n", *pen);
*pen++;
}
}
I'm trying to grasp the idea of pointers with string. I ran both of the codes and got the same result, but I got a warning on the 2nd version of the code with *pen++ but still was able to run.
What is each of them doing and how come it gave me the same output?

Answer 1

According to the rules on operator precedence, the line
*pen++;
is equivalent to
*(pen++);
which means the * does nothing. So it is doing exactly the same thing as the line
pen++;
in the first program.
Also, it is important to note that the line
char mine[5] = "hello";
is not doing what you expect. You are initializing a character array of length 5 with a string literal of length 6 (including the terminating null character). This means the array does not contain sufficient space for the terminating null character.
Therefore, you should change the line to the following:
char mine[6] = "hello";
Alternatively, in order to make the compiler automatically allocate a sufficient amount of memory for the initialization, you can just write the following:
char mine[] = "hello";

Answer 2

pen++; is a statement consisting of one expression pen++. This expression's value is pen and the side effect is that pen is incremented.
*pen++ is a statement constisting of one expression *pen++. The expression's value is *pen and the side effect is that pen is incremented.
When an expression is used as a statement, then the value of the expression is ignored, only the side effects are relevant/observable. So in your case it is irrelevant if pen or *pen is the value, the side effect of incrementing pen is identical in both cases. Thus in your program both variants have the same observable effect. Yet it does not make sense to write *pen++ if you don't want to use the value. Then you should just write pen++, or even better ++pen.