How to print elements in a vector c++ - c++

Question

I am having trouble with my void print function to print out this vector. I'm not quite sure what it is talking about with "std::allocator. I get these errors:
st1.cpp: In function ‘void Print(std::vector<int, std::allocator<int> >)’:
st1.cpp:51: error: declaration of ‘std::vector<int, std::allocator<int> > v’ shadows a parameter
Here is the file:
#include <iostream>
#include <string>
#include <vector>
#include <stack>
#include <algorithm>
using namespace std;
void Initialize();
void Print();
int main()
{
stack<string> s1, s2;
s1.push("b");
s2.push("a");
if (s1.top() == s2.top())
{
cout << "s1 == s2" << endl;
}
else if (s1.top() < s2.top())
{
cout << "s1 < s2" << endl;
}
else if (s2.top() < s1.top())
{
cout << "s2 < s1" << endl;
}
else
{
return 0;
}
vector<int> v;
Initialize();
Print();
}
void Initialize(vector<int> v)
{
int input;
cout << "Enter your numbers to be evaluated: " << endl;
while(input != -1){
cin >> input;
v.push_back(input);
//write_vector(v);
}
}
void Print (vector<int> v){
vector<int> v;
for (int i=0; i<v.size();i++){
cout << v[i] << endl;
}
}
I just want to print v out to the screen. Any help?

Answer 1

Your function declaration and definition are not consistent, you want to generate vector from Initialize, you can do:
void Initialize(vector<int>& v);
To print vector:
void Print(const vector<int>& v);
Now you call:
vector<int> v;
Initialize(v);
Print(v);
Don't forget to change function definition of Initialize, Print to match the new signature I provided above.
Also you are redefining a local variable v which shadows function parameter, you just need to comment out that line, also pass vector by const ref:
void Print (const vector<int>& v){
//vector<int> v;
for (int i=0; i<v.size();i++){
cout << v[i] << endl;
}
}

Answer 2

You have to pass by const reference and remove the extraneous vector.
void Print(const std::vector<int>& v){
for(unsigned i = 0; i< v.size(); ++i) {
std::cout << v[i] << std::endl;
}
}
Another way to print it out would be to use iterators like so:
void Print(const std::vector<int>& v) {
std::vector<int>::iterator it;
for(it = v.begin(); it != v.end(); ++it) {
std::cout << (*it) << '\n';
}
}
Or in C++11 you can do it like so:
void Print(const std::vector<int>& v) {
for(auto& i : v)
std::cout << i << '\n';
}
I don't think your Initialize() function works like you expect it to. It seems to just make a copy and then discards it, not modifying any values of the existing vector.

Answer 3

Leveraging c++ std's 11 onwards, this could be acheived in one line as shown below.
std::for_each(v.begin(),v.end(),[](const int &i) { std::cout << i; });
This code runs a for loop using std::vector iterators from begin() to end(), serially feeding the lambda/[] function the required argument to be printed.