Measuring the length of a string with a for loop

Hey!
So I have a simple program that measures the length of a string using a for loop.

Code:

---

#include <stdio.h>

int main(void) {
    unsigned i;
    char str[16] = "ABBA";

    for (i = 0; str[i] != '\0'; ++i);

    printf("Len: %u", i);

    return 0;
}

---

It works fine, but there's one thing I can't wrap my head around. If I set the initial value of i to 1 inside of the loop the program still outputs 4 in fact it always outputs 4. Even if I set the value of i to something like 2 or 3.

Here's the thing, shouldn't it output 3 if i starts at str[1]? The loop should start at 'B' and finish at 'A' which is three characters. But that's not the case for some reason. Can anybody explain this to me?

Thanks in advance.

for (i = 1; str[i] != '\0'; ++i);

Is no different to this, having gone round the loop once.
for (i = 0; str[i] != '\0'; ++i);

Compare with

Code:

---

int main(void) {
    unsigned i, count;
    char str[16] = "ABBA";
 
    for (count = 0, i = 0; str[i] != '\0'; ++i, ++count);
 
    printf("Len: %u", count);
 
    return 0;
}

---

Now you'll see a difference whether you start at i=0 or i=1

Code:

---

int stringLength(char *string) {
    int i = 0;
    while (string[i] != '\0') i++;
    return i;
};

---

I want to point out that setting i to values above 0 does actually do something bad in your case: if your string's length is less than the initial value of i, you will be accessing memory you shouldn't be accessing, potentially causing a segfault or worse side effect, including returning the length of a different string!