C++ STL - vector - modifying data by operator[], erase(), insert()

ABOUT Vector index

vector - modify data

at : access specified element with bounds checking
operator[] : access specified element

vector <int> v;
for(int i=1;i<=10;i++){
   v.push_back(i);
}

v.at(4) = -1;
v[4] = 77;

• at and operator[] both return a reference to the indexed element

• you’d better take the habit to use at, less idiomatic, but bound-checking is priceless

• A much better way is to use at(...). This will automatically check for out of bounds behaviour and break throwing an std::out_of_range.

v.at(10) = 9;

• We will get:
  terminate called after throwing an instance of ‘std::out_of_range’ what(): vector::_M_range_check: __n (which is 10) >= this->size() (which is 4)

vector - erase : erase data

vector <int> v;
for(int i=1;i<=10;i++){
   v.push_back(i);
}

int count = 0;
for(vector<int>::iterator it = v.begin(); it != v.end(); it++){
    if(count == 5){ // in case of the index is 5 --> data will be erased
        it = v.erase(it);
        break;
    }else{
        count++;
    }
}

vector - insert : insert data

vector <int> v;
for(int i=1;i<=10;i++){
   v.push_back(i);
}

int count = 0;
for(std::vector<int>::iterator it = v.begin(); it != v.end(); it++){
    if(count == 5){// in case of the index is 5 --> data will be inserted
        v.insert(it,6);
        break;
    }else{
        count++;
    }
}