problem with for loop

[indr]

the following is the code...
#include<iostream>
#include<iomanip>
using namespace std;

int main()
{
float start_temp,stop_temp;
float step,F,C;
cout<<"start temperature:";
cin>>start_temp;
cout<<"stop temperature:";
cin>>stop_temp;
cout<<"step temperature:";
cin>>step;
float i=0;
cout<<setw(10)<<"celsius"<<setw(15)<<"fahrenheit"<<endl;
cout<<setw(25)<<"celsius"<<setw(15)<<"fahrenheit"<<endl;
for(i=start_temp;i<=stop_temp;i=i+step)
{
C=(5.0/9.0)*(i-32);
F=32+(9.0/5.0)*i;
cout<<setprecision(2);
cout.setf(ios::fixed);
cout<<setw(10)<<C<<setw(10)<<i<<setw(10)<<F<<endl;

}

}
and the output for the above code is:

start temperature: 0
stop temperature: 11
step temperature: 1.1

-17.78 0.00 32.00
-17.17 1.10 33.98
-16.56 2.20 35.96
-15.94 3.30 37.94
-15.33 4.40 39.92
-14.72 5.50 41.90
-14.11 6.60 43.88
-13.50 7.70 45.86
-12.89 8.80 47.84
-12.28 9.90 49.82
-11.67 11.00 51.80

but i am not able to print the last line of output.i.e.,-11.67 11.00 51.80
i dont know why it is not printing the last line of output..
but it is working for the following output:
start temperature: 60
stop temperature: 80
step temperature: 2

15.56 60.00 140.00
16.67 62.00 143.60
17.78 64.00 147.20
18.89 66.00 150.80
20.00 68.00 154.40
21.11 70.00 158.00
22.22 72.00 161.60
23.33 74.00 165.20
24.44 76.00 168.80
25.56 78.00 172.40
26.67 80.00 176.00

[Luiwtf]

It's because floating point numbers tend not to be completely accurate, the variable i, is actually 11.000001 when the loop tests for the condition, which means it fails since it's more than 11.

Using doubles, rather than floats fixes it (as i is actually 10.9999999999999998)

Or you can just add a small number to:

for(i=start_temp;i<=stop_temp + NUMBERHERE;i=i+step)

like say 0.00001, which will account for any innaccuracies due to using floating point numbers.

Edit - I'd go for the second option btw, as even using a double, you will probably still get errors when using different numbers

Oh, and there may be a better way to do it, but I'm just learning c++ atm ;)

[Galik]

Comparing floating point numbers for equivalence is dangerous because of tiny inaccuracies. For that reason you should avoid doing a <= in your loop.

It is better to look at the range of values you want to iterate over and always compare less-than (<).