Using push_back for vector in c++ - c++

Question

I am having trouble using push_back for vectors in c++.
My vector is named data.
In my loop I want to add 50 to data[i].getQuantity then push_back to data
These are things that I have tried.
data.push_back(data[i].getQuantity());
and
float myFloat = data[i].getQuantity() + 50;
data.push_back(data[i].getQuantity(myFloat));
data.push_back(myFloat);
The error is saying
No function to call to push_back
Here is my code:
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <vector>
#include <iterator>
struct Input
{
friend std::istream& operator >>(std::istream& inp, Input& item);
friend std::ostream& operator <<(std::ostream& outp, Input const& item);
std::string group;
std::string total_pay;
float quantity;
// default constructor. sets up zero-elements
Input() : group(), total_pay(), quantity()
{
}
Input(std::string groupIn, std::string total_payIn, float quantityIn) :
group(std::move(groupIn)),
total_pay(total_payIn),
quantity(quantityIn)
{
}
// Accessors
std::string const& getGroup() const { return group; }
std::string getTotalPay() const { return total_pay; }
float getQuantity() const { return quantity; }
};
// global free function for extracting an Input item from an input stream
std::istream& operator >>(std::istream& inp, Input& item)
{
return (inp >> item.group >> item.total_pay >> item.quantity);
}
// global operator for inserting to a stream
std::ostream& operator <<(std::ostream& outp, Input const& item)
{
outp
<< item.getGroup() << ", "
<< item.getTotalPay() << ", "
<< item.getQuantity();
return outp;
}
struct ctype : std::ctype<char>
{
static mask* make_table()
{
static std::vector<mask> table(classic_table(),
classic_table() + table_size);
table[','] |= space;
return &table[0];
}
ctype() : std::ctype<char>(make_table()) { }
};
int main() {
std::fstream infile("employee.dat");
std::vector<Input> data;
std::string line;
try {
while (std::getline(infile, line))
{
std::istringstream iss(line);
Input inp;
iss.imbue(std::locale(iss.getloc(), new ctype));
while (iss >> inp) // calls our extraction operator >>
data.push_back(inp);
if (iss.fail() && !iss.eof())
std::cerr << "Invalid input line: " << line << '\n';
}
// dump all of them to stdout. calls our insertion operator <<
std::copy(data.begin(), data.end(),
std::ostream_iterator<Input>(std::cout,"\n"));
std::ofstream outp("output.dat");
for(int i = 0; i < data[i].getQuantity(); i++)
{
float myFloat = data[i].getQuantity() + 50;
data.push_back(myFloat);
outp << data[i].getGroup() << ',' << data[i].getTotalPay() << ',' << data[i].getQuantity() + 50 << '\n';
}
} catch (std::exception& e) {
std::cout << "There was an error: " << '\n';
return 1;
}
return 0;
}

Answer 1

Your vector is of type std::vector<Input>. That means you can only put objects of type Input into it. You can't push_back a float into such a vector.
If your intention is to create a new Input object and push that back into your vector, you could do something like
data.push_back(Input(data[i].getGroup(), data[i].getTotalPay(), data[i].getQuantity() + 50))
On the other hand, if you are simply trying to modify an element in data without adding a new element to data, you could just do
data[i].quantity += 50;
This works because you use a struct rather than a class. In a struct, variables default privacy level is public. If you wanted to use a class, or you just don't want to directly access the struct members, you would have to create a setter function for quantity.