Thread: Question about a certain code with the C++ syntax

I was wondering if it is possible to do a sum of vectors with a range.

The bold is where I am concerned about the syntax. Thanks.

Code:

//Running Mean for 3 points with even weights

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




int main ()


{
float numberofterms; 
cout<<"Enter the number of terms you want: " <<endl;
cin>>numberofterms;   
vector<float> temperature(numberofterms); //Define a vector of 5 floats
int vectorlength;
vector<float> movingavg;


int index; //Loop counter
float average;


for (index==0; index<numberofterms; index++)
{   
    cout<<"Enter temperature you want to input in Celsius"<<(index+1);
    cout<<": ";
    cin>>temperature[index];
     
     if (index==0)
     { movingavg[index]=temperature[index];
       cout<<"Temperature [1]= "<<temperature[0]<<" C"<<endl;
       continue;
     }
     else if (index==numberofterms-1)
     {
     movingavg[index]=temperature[index];
     cout<<"Temperature ["<<numberofterms<<"]= "<<temperature[numberofterms-1]<<" C"<<endl;
     continue;
     }
      average= sum((temperature[index-1:index+1]/3));
    movingavg[index]=average;
    cout<<"Temperature ["<<index+1<<"] = "<<average<<" C"<<endl;
    cout<<"The original temperature ["<< index+1<<"]"<<temperature[index]<<"] C has been replaced." <<endl;
}






system ("PAUSE");


return 0;


}

>> average= sum((temperature[index-1:index+1]/3));

Couple things about this. vectors do not have python-like slicing, but you can call a function called accumulate(). Also it is mathmatically important to sum before you divide.

Oh! Can this work then?

sum = accumulate(temperature.begin(),temperature.end());
average=sum/3;

If you read the help page, it says accumulate() has to have a third argument that specifies where to start adding from. It also specifies the type of the return value, so you want it to be float. Other than that, it's ok.

You should probably use the size of your vector instead of the magic number 3 when doing your average. You also can't use array notation [] to insert elements into an empty vector, you need to either construct movingavg with a size, like you did with temperature, or use push_back() to insert a new element.

Jim

Originally Posted by jimblumberg

You should probably use the size of your vector instead of the magic number 3 when doing your average. You also can't use array notation [] to insert elements into an empty vector, you need to either construct movingavg with a size, like you did with temperature, or use push_back() to insert a new element.

Jim

Confused on what your saying Jim. Getting an error. The user inputs the number but the cmd prompt exits. Instead of doing the rest of the program. What's wrong?

Code:

//Running Mean for many points with even weights


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




int main ()


{
float numberofterms; 
cout<<"Enter the number of terms you want: " <<endl;
cin>>numberofterms;   
vector<float> temperature(numberofterms); //Define a vector of 5 floats
int vectorlength;
vector<float> movingavg;


int index; //Loop counter
float average;


for (index==0; index<numberofterms; index++)
{   
    cout<<"Enter temperature you want to input in Celsius"<<(index+1);
    cout<<": ";
    cin>>temperature[index];
     
     if (index==0)
     { movingavg[index]=temperature[index];
       cout<<"Temperature [1]= "<<temperature[0]<<" C"<<endl;
       continue;
     }
     else if (index==numberofterms-1)
     {
     movingavg[index]=temperature[index];
     cout<<"Temperature ["<<numberofterms<<"]= "<<temperature[numberofterms-1]<<" C"<<endl;
     continue;
     }
      average= ((temperature[index-1+index+index+1]/temperature.size()));
    movingavg[index]=average;
    cout<<"Temperature ["<<index+1<<"] = "<<average<<" C"<<endl;
    cout<<"The original temperature ["<< index+1<<"]"<<temperature[index]<<"] C has been replaced." <<endl;
}






system ("PAUSE");


return 0;


}

Part of your problem is you are trying to use your vector movingavg that contains no elements. You can't use the operator= to insert elements into a vector.

Getting an error.

And your error is???

Jim

Have you tried running this program through your debugger? If your program is crashing the debugger will tell you exactly where it detected the problem. Then you can view the values of your variables at the time of the crash to help isolate the problem.

However, unless you fixed the problem with your movingavg vector, this is where you need to start.

Jim

Is there any examples I can look at that can help me fix the problem?

Yes, look at the difference between:

Code:

vector<float> temperature(numberofterms); //Define a vector of 5 floats
vector<float> movingavg;

Your temperature vector has numberofterms elements. Your movingavg vector has no elements. Before you can use a vector element it must exist. Therefore in the following:

Code:

   temperature[0] = 100.0;  // This will work.
   movingavg[0] = 100.0;   // This will not work.

Your vector element must exist before you can access it with the array notation. There are three ways to add elements to your vector, when you construct the vector use the size option, (like you did with temperature), the resize() member function, or use the push_back() member function. Since you know how many elements you want your vector to contain I recommend the first option.

Jim

oh ok! So here's what I did in the beginning...

vector<float>movingavg(numberofterms);


Would this resolve the problem?

so here's what I have so far:

Code:

//Running Mean for 3 points with even weights


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




int main ()


{
float numberofterms; 
cout<<"Enter the number of terms you want: " <<endl;
cin>>numberofterms;   
vector<float> temperature(numberofterms); //Define a vector of 5 floats
int vectorlength;
vector<float> movingavg(numberofterms);


int index; //Loop counter
float average;


for (index==0; index<numberofterms; index++)
{   
    cout<<"Enter temperature you want to input in Celsius"<<(index+1);
    cout<<": ";
    cin>>temperature[index];
     
     if (index==0)
     { movingavg[index]=temperature[index];
       cout<<"Temperature [1]= "<<temperature[0]<<" C"<<endl;
       continue;
     }
     else if (index==numberofterms-1)
     {
     movingavg[index]=temperature[index];
     cout<<"Temperature ["<<numberofterms<<"]= "<<temperature[numberofterms-1]<<" C"<<endl;
     continue;
     }
      average= ((temperature[index-1+index+index+1]/temperature.size()));
    movingavg[index]=average;
    cout<<"Temperature ["<<index+1<<"] = "<<average<<" C"<<endl;
    cout<<"The original temperature ["<< index+1<<"]"<<temperature[index]<<"] C has been replaced." <<endl;
}






system ("PAUSE");


return 0;


}

Is this just part of the problem or will the inside code need to be changed as well?