Using Auto in a for loop

Hi all,

i was doing the following:

Code:

---

for (int i = 0; i < numbers.capacity(); i++) {
        numbers.push_back(rand() % 30);
}

---

so i got the warning:

Code:

---

warning C4018: '<': signed/unsigned mismatch

---

i get the same warning if i use "auto" instead of "int" :

Code:

---

for (auto i = 0; i < numbers.capacity(); i++) {
        numbers.push_back(rand() % 30);
}

---

i get only rid of the warning when i use "unsigned int".

My question:
itsn't that where "auto" is supposed to help? so that i don't need to bother aboutthe data type ?
what i am i doing wrong? is there some best practice where not to use "auto" ?

i used a lot with range based for loops, it works fine

Thanks in advance

The type of 0 is int, so using auto here still causes i to be of type int. If you really wanted to, you could write:

Code:

---

for (decltype(numbers.capacity()) i = 0; i < numbers.capacity(); i++)

---

But that seems unnecessarily repetitive to me. Maybe:

Code:

---

auto capacity = numbers.capacity();
for (decltype(capacity) i = 0; i < capacity; ++i)

---

EDIT:
I might test this later to be sure, but the thought came to mind that you might be able to use generate_n with back_inserter to accomplish this:

Code:

---

std::generate_n(std::back_inserter(numbers),
                numbers.capacity(),
                []() { return rand() % 30; });

---

Quote:

---

The type of 0 is int, so using auto here still causes i to be of type int

---

alright alright, now i got it, and thanks for the alternatives.

generate_n with back_inserter are very new to me :)