warning C4018: '<': signed/unsigned mismatch ONLY when I include Identical Functions - c++

Question

I am lost, when I ran my program last night it ran fine. When I added the power() function, suddenly lines which ran fine without adding the new code now trigger an error message:
warning C4018: '<': signed/unsigned mismatch
Why?
I feel I don't have the chops to explain this, so please follow the code below.
PLEASE RUN THE CODE WITH AND WITHOUT THIS power() FUNCTION. When run with the power() function, it makes error C4018 on the for loops in the exam() function! When run without the power() function, it runs FINE!!
#include <string>
#include <cstdlib>
#include <iostream>
#include <vector>
#include <cmath>
#include <numeric>
using namespace std;
///the offending function///
double power(double base, int exponent)
{
double product;
//double base; int exponent;
std::cout << "enter a value for base: " << endl;
std::cin >> base;
std::cout << "enter exponenent: " << endl;
std::cin >> exponent;
double result = 1;
for (int i = 0; i < exponent; i++)
{
result = result * base;
//product = base exponent;
}
std::cout << product;
return product;
}
///after here, things run fine if you X out the aforementioned function! Wow!
void exam()
{
std::vector<int> scores;
int F;
F = 0; //string names;
std::cout << "enter exam scores int:" << endl;
//std::vector <string> names;
while (F != -1)
{
std::cout << "Enter a new exame score:" << endl;
std::cin >> F;
scores.push_back(F);
}
if (F == -1)
{
std::cout << "end of score entering" << endl;
}
for (int i = 0; i < scores.size(); i++)
{
std::cout << scores[i];
}
/*
while (i < scores.size())
{
std::cout << scores[i];
i++;
}
*/
std::cout << "yay you made this work!!!!!!!!!!!!!" << endl;
}
int multiply()
{
int a;
int b;
a = 8;
b = 4;
std::cout << a * b << endl;
std::cout << "f*** yeah" << endl << endl;
return 0;
}
void test()
{
std::vector<int> newvector;
int T;
std::cout << "enter vector variables: " << endl;
std::cin >> T;
newvector.push_back(T);
while (T != -1)
{
std::cout << "enter new vector variables T " << endl;
std::cin >> T;
newvector.push_back(T);
if (T == -1)
{
newvector.pop_back();
}
}
std::cout << "end of NewVector data inputs:" << endl;
for (int W = 0; W < newvector.size(); W++)
{
std::cout << newvector[W] << endl;
}
}
int main()
{
power(2, 3);
exam();
/*int result = multiply();
std::cout << "endl ;" << endl;
test();
system("pause"); */
multiply();
string name;
int a;
std::cout << "enter a variable for your name: " << endl;
std::getline(cin, name);
if (name == "aaron")
{
std::cout << " what a dumb name, aAron?" << endl;
}
else if (name == "todd")
{
std::cout << "what a dottly name, Todd" << endl;
}
else
{
std::cout << "your name = " << name << endl;
}
//std::vector <string>
std::vector<int> asdf;
std::cout << "enter an int for a" << endl;
std::cin >> a;
asdf.push_back(a);
while (a != -1)
{
std::cout << "enter another A: " << endl;
std::cin >> a;
asdf.push_back(a);
if (a == -1)
{
asdf.pop_back();
}
} //set var; checks if d<size(); if so, JUMP to std::cout<<; when finished with body, find after size(); == "d++", then refer back to declaration)
/*/ for(int G = 0; G<asdf.size(); G++)
{
std::cout << asdf[G] << endl;
} */
for (int i = 0; i < asdf.size(); i++)
{
std::cout << asdf[i] << "f*** it works!!!!!! " << endl;
}
for (int d = 0; d < asdf.size(); d++)
{ //htt ps://youtu.be/_1AwR-un4Hk?t=155
std::cout << asdf[d] << ", ";
}
std::cout << endl;
std::cout << std::accumulate(asdf.begin(), asdf.end(), 0);
//std::cout<<
system("pause");
return 0;
}

Answer 1

The presence of the power function should have no effect on this problem. Possibly you aren't seeing the warnings because without the power function the program does not compile.
In
for (int W = 0; W < newvector.size(); W++)
newvector.size() returns an unsigned integer. int W is a signed integer. You're getting exactly what you asked for.
You can change int W to vector<int>::size_type W (but the less verbose size_t W should also work) to make the error message go away, but this is an error where you would likely have to add more than 2 billion items to the vector to see manifest.
Solution:
for (vector<int>::size_type W = 0; W < newvector.size(); W++)
However this is a good place for a range-based for loop
for (const auto &val: newvector)
{
std::cout << val << endl;
}
By letting the compiler figure out all the sizes and types your life is much easier.
This is repeated several times throughout the code.

Answer 2

Re: WHEN RUN, It makes error C4018 -
YOU made that error (warning, actually), not "it".
That warning is reported by compiler, so you haven't run anything yet...
Your newly added function uses uninitialized variable product; in my version of Visual Studio it is an error.