Can someone help me with this C++ code?

[RP65]

I am a beginner with C++ can someone help me with this code? I can't figure out why the rainfall inches are not adding up.

#include <iostream>
#include <iomanip>
using namespace std;

int main()
{
int numYears = 0;
float totalRainfall = 0.0, avgRainfall = 0.0, rainfall = 0.0;
const int MONTH = 12;

cout << "Please enter number of years:" << endl;
cin >> numYears;
while (numYears < 1)
{
cout << "Number of years must be at least 1. Please re-enter: ";
cin >> numYears;
}
for (int i = 1; i <= numYears; i++)
{
for (int months = 1; months <= MONTH; months++)
{
cout << "Please enter the rainfall for " << months << "month: ";
cin >> rainfall;
}
while (rainfall < 0)
{
cout << "The rainfall cannot be a negative number. Please re-enter: ";
cin >> rainfall;
}
totalRainfall =+ rainfall ;
}
cout << "\nNumber months: " << numYears * MONTH << endl;
cout << "Total rainfall: " << setprecision(2) << fixed << totalRainfall
<< " inches." << endl;
cout << "Average rainfall: " << setprecision(2) << fixed
<< totalRainfall / (numYears * MONTH) << " inches." << endl;
cin.get();
return 0;
}

[keskiverto]

totalRainfall =+ rainfall ;
Recheck the syntax of that operator.