Vector of structs initialization

Create vector, push_back element, then modify it as so:

struct subject {
    string name;
    int marks;
    int credits;
};


int main() {
    vector<subject> sub;

    //Push back new subject created with default constructor.
    sub.push_back(subject());

    //Vector now has 1 element @ index 0, so modify it.
    sub[0].name = "english";

    //Add a new element if you want another:
    sub.push_back(subject());

    //Modify its name and marks.
    sub[1].name = "math";
    sub[1].marks = 90;
}

You cant access a vector with [#] until an element exists in the vector at that index. This example populates the [#] and then modifies it afterward.

If you want to use the new current standard, you can do so:

sub.emplace_back ("Math", 70, 0); // requires a fitting constructor, though

or

sub.push_back ({"Math", 70, 0}); // works without constructor

.