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..

[mike_2000_17]

that simple: floating point values on a computer always approximate the real value to some round-off error (about to the 7th significant digit for float and to the 20th significant digit for double). So the comparison i<=stop_temp is not going to work all the time because even when i is 11, it might actually be 11.0000034 or something like that and thus, not equal to stop_temp (which also will not necessarily be exactly 11 either).

So to fix the problem, use an integer-valued iterator, like this:

int iter = ceil((stop_temp - start_temp) / step); //ceil will get the smallest integer value that is greater than "(stop_temp - start_temp)/step".
  for(i=start_temp; iter>=0 ;iter--,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;

  }

EDIT: ceil is found in <cmath> by the way. (so you need also #include <cmath> at the start)

[indr]

hi thanks for your reply...
but when i used ceil as integer.. it showed me an error.. so i declared iter as float...
because all the variables in the program are float...
but it only worked for the input...
input:
start temperature: 0
stop temperature: 11
step temperature: 1.1
output:
-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 it did not work for the following input...
input:
start temperature: 30
stop temperature: 60
step temperature: 3.5
output:
-1.11 30.00 86.00
0.83 33.50 92.30
2.78 37.00 98.60
4.72 40.50 104.90
6.67 44.00 111.20
8.61 47.50 117.50
10.56 51.00 123.80
12.50 54.50 130.10
14.44 58.00 136.40

extra lines of output are displayed for the above input.. the extra line is 16.39 61.50 142.70

[mike_2000_17]

You replaced one problem with the same problem. The main point with my solution was that you cannot do an exact number of iterations with a float because float is not exact, regardless of how you put it. You need to use an integer value to count the iterations, not a float.

If the ceil function gave an error like "cannot convert double to int" then use "int iter = int(ceil(..));" to explicitly cast to int.

[indr]

yes i type casted in to int..
int iter=(int)ceil((stop_temp-start_temp)/step)
but still i am getting an extra line for the second set of input...

[mike_2000_17]

To get rid of the extra line, use this instead:

int iter = (int)floor((stop_temp - start_temp + step / 2.0) / step);

[indr]

nope its not working still..:(((((((((((((((((
i am still getting the extra line for the last set of inputs....

[Luther von Wulf]

floats can be used as a counter, but you must be very careful in comparing them because they are approximations of values and have inaccuracy where two values that seem the same are not exactly the same. A fuzzy comparison is usually used for floating point. Here is your code with the fuzzy comparisons added.

#include<iostream>
#include<iomanip>
#include<limits>
#include<math.h>
using namespace std;

inline bool less_than(float lhs, float rhs) {
    float sig = fabs(lhs) < fabs(rhs) ? fabs(rhs) : fabs(lhs);
    return rhs-lhs > sig * numeric_limits<float>::epsilon();
}

inline bool equal_to(float lhs, float rhs) {
    float sig = fabs(lhs) < fabs(rhs) ? fabs(rhs) : fabs(lhs);
    return fabs(lhs-rhs) <= sig * numeric_limits<float>::epsilon();
}

inline bool less_or_equal(float lhs, float rhs) {
    return less_than(lhs, rhs) || equal_to(lhs, rhs);
}

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; less_or_equal(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;
    }
}