C++ :: IntelliSense - Expression Must Have Integral Or Unscoped Enum Type

So far I have the following code:

// Purpose: To write a program that displays the number of millimeters higher the current level the ocean level will be in
// in 5, 7, and 10 years.

# include <iostream>
# include <string>
using namespace std;
int main() {
float X = 10;
string Y="";

[Code] ....

But I get the following error message:

IntelliSense: expession must have integral or unscoped enum type

three times in a row for lines 25, 27, and 29 and I don't understand or know why?

In case the purpose does make sense here are the directions:

2.7: Ocean Levels

Assuming the ocean’s level is currently rising at about 1.5 millimeters per year, write a program that displays

•The number of millimeters higher than the current level that the ocean’s level will be in 5 years,
•The number of millimeters higher than the current level that the ocean’s level will be in 7 years,
•The number of millimeters higher than the current level that the ocean’s level will be in 10 years,

Output labels:

Each value should be on a line by itself, preceded by the a label of the form:

In X years the ocean's level will be higher by Y millimeters.

where X is the number of years (5, 7 or 10) and Y is the value you calculate.