my professior gave us an example program for a fiter.. but I can't get it to work...

my professor gave us an example program for a filter.. but I can't get it to work...
This is my 1st time using C++ and before we where learning C... so I can't easily see why it doesn't work.... this is an example and shouldn't have errors but ya.. it does so can anyone help me? thanks

Code:

---

#include <iostream>
using namespace std;

int main()
{
    int i, numpts;
    double input[25]; //store values for filtering
    cout << "enter number of points: ";
    cin >> numpts;
    for (int i = 0; i < numpts; i++)
    {
        cout << "Enter a point: ";
        cin >> input[i];
    }
    double output[25]; //store filtered results
    double alpha = .5;// 0 < alpha 1
    output[0] = input[0];
    for (int i = 1; i < numpts; i++)
        output[i] = alpha*input[i]+(1-alpha)*output[i-1];
    for (int i = 0; i < numpts; i++)
    {
        cout << "Output " <<i << " is " << output[i];
        cout << "\n";
    }
    return 0;
}

---

.5 needs to be 0.5, but other than that, what errors does the compiler give?

Code:

---

>ch -u "simpleFilt.cpp"   
ERROR: maybe missing ';' before '='
ERROR: with unnecessary identifier 'i' in casting operator
ERROR: incompatible types for casting operation, casting void to int
ERROR: missing ';' in for-loop
ERROR: syntax error before or at line 12 in file 'simpleFilt.cpp'
  ==>:    for (int i = 0; i < numpts; i++)
  BUG:    for (int i = 0; i <<== ???
ERROR: multiple operators together
ERROR: syntax error before or at line 12 in file 'simpleFilt.cpp'
  ==>:    for (int i = 0; i < numpts; i++)
  BUG:    for (int i = 0; i <<== ???
ERROR: multiple operators together
ERROR: syntax error before or at line 12 in file 'simpleFilt.cpp'
  ==>:    for (int i = 0; i < numpts; i++)
  BUG:    for (int i = 0; i <<== ???
ERROR: multiple operators together
ERROR: syntax error before or at line 12 in file 'simpleFilt.cpp'
  ==>:    for (int i = 0; i < numpts; i++)
  BUG:    for (int i = 0; i <<== ???
ERROR: multiple operators together
ERROR: syntax error before or at line 12 in file 'simpleFilt.cpp'
  ==>:    for (int i = 0; i < numpts; i++)
  BUG:    for (int i = 0; i <<== ???
ERROR: multiple operators together
ERROR: syntax error before or at line 12 in file 'simpleFilt.cpp'
  ==>:    for (int i = 0; i < numpts; i++)
  BUG:    for (int i = 0; i <<== ???
ERROR: multiple operators together
ERROR: syntax error before or at line 12 in file 'simpleFilt.cpp'
  ==>:    for (int i = 0; i < numpts; i++)
  BUG:    for (int i = 0; i <<== ???
ERROR: multiple operators together
ERROR: syntax error before or at line 12 in file 'simpleFilt.cpp'
  ==>:    for (int i = 0; i < numpts; i++)
  BUG:    for (int i = 0; i <<== ???
ERROR: multiple operators together
ERROR: syntax error before or at line 12 in file 'simpleFilt.cpp'
  ==>:    for (int i = 0; i < numpts; i++)
  BUG:    for (int i = 0; i <<== ???
ERROR: multiple operators together
ERROR: syntax error before or at line 12 in file 'simpleFilt.cpp'
  ==>:    for (int i = 0; i < numpts; i++)
  BUG:    for (int i = 0; i <<== ???
ERROR: maybe missing '}' at the end of program at line 12 or there is an extra '{' in other place in file 'simpleFilt.cpp'
ERROR: cannot execute command 'simpleFilt.cpp'
>Exit code: -1

---

its really weird... cuz I tried it in a different compiler and it work so I dunno...

Code:

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for (int i = 0; i < numpts; i++)

---

You can start by trying to get rid of those.

Code:

---

//Here is the original code with comments.
//No changes to the code, as to help you better understand the syntax
/* Even if you manage to compile this code sample, your program will crash
  as soon as any invalid user input is entered.*/

//Header files - All the stuff your program will use.
#include <iostream>

//Name spaces for api's being used. Declaired in line 7.
using namespace std;

//Main fuction. This is where your program starts.
// main is better as // int main(int argc, char* argv);
int main()
{
    int    i,              //Iterator for User Input
          numpts;        //Number of values the user will input
    double input[25];      //store values for filtering : values entered by the user

    cout << "enter number of points: "; //Display request to user
    cin >> numpts;                      //Get User Input: array size
   
    //User input loop
    for (int i = 0; i < numpts; i++) /* C++ allows you to create a value anytime you want,
                                        Error 1: Please look at line 24 and 16 and tell me what you see
                                        Error 2: numpts (line 17) is used on line 21 and again on 24
                                        i'll help show you the problem when you start getting the basics. */
    {
        cout << "Enter a point: "; //output to user
        cin >> input[i];          //input from user
    }

    /*The syntax of c++ allows you to declare a value any
        time you want. But does have limits.
    */
    double output[25]; //store filtered results
    double alpha = .5;// 0 < alpha 1
    output[0] = input[0]; /* Store the first element of the user input array(line 18)
                                into the first element of the output array(line36)*/
                               
    /* This loop does some math on the users input then stores the results as output. */
    for (int i = 1; i < numpts; i++)                        //Please see note on line 25
        output[i] = alpha*input[i]+(1-alpha)*output[i-1];  /*Simple math. alpha*x+(1-alpha)*y
                                                                'x' is the user input in the order given by the user
                                                                'y' is the last output of the loop*/
                                                               
    for (int i = 0; i < numpts; i++)    //Please see not on line 42
    {
        //Display results of the loop chain to user
        cout << "Output " <<i << " is " << output[i]; // C++ allows for you to easily compine multiple function calls.       
            /*  Output 0 is 12.345 */ //Example output.
       
        cout << "\n"; //output a newline to the screen. Please see note on line 50
    }
    return 0; //Program is finished, exit main();
}

---

As you fix the logic problems your compiler has flaged as a "bug" you should be able to compile
and recive more detailed error messages about the problem.
As well as fix the possible buffer overrun error in the code.

thanks, this is very helpful! I don't understand all of it yet, but I hope to learn to soon. thanks

ok I'm tryin to practice before doing homework...cuz I still don't get it and I was trying to do a simple program but I can't seem to fix it....:o:confused:

Code:

---

#include <iostream>

using namespace std;

int main()
{
    double data[11];
    int i;
    cout << "How many data ponits 1 to 10?" << endl;
    cin >> i ;
        if (i < 1 | i > 10)
            {
                cout << "worng amount of data points please try again" << endl;
                return 0;
            }

        if (i=0;1<i<10;i++)
            {
                cout << "Enter data ponit:"<<endl;
                cin >> data[i];
            }
    return 0;

---

it says error line 17 ... why?:frown:
thanks for any help!:)

Code:

---

        if (i=0;1<i<10;i++)

---

you have used an if statement where it looks like you wanted a for statement

Code:

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for( i=0; 1 < i < 10; i++)

---

Also on line 11. '|' and '||' are two different things.
you need '||' there, the first you have is a bitwise operator.

thank you again, whats a bit wise operator?

Cprogramming.com - Tutorials - Bitwise Operators and Bit Manipulations in C and C++

Code:

---

for(i=0;1<i<10;i++)

---

Lets read this statement in english

FOR this loop, 'i' starts at zero;
loop untill the next statement is false. One is less than 'i'. And 'i' is less than ten.
Increment 'i'.
Loop;

When the loop start will your statement 1 < i < 10 be true or false?

Quote:

---

Originally Posted by King Mir

.5 needs to be 0.5

---

Picky me: No, 0.5 can also be written as ".5", just as 1.0 can be written as "1.". It just that the full forms are more readable. So corrected, the sentence would be, ".5 should be 0.5".

Ok, I'm done. :)

Quote:

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Originally Posted by Cess

Code:

---

if (i=0;1<i<10;i++)

---

---

As Nor pointed out that "if" should be "for". However there is another problem here. Notation in maths often gets sloppy, and a < x < b meaning x is between a and b is a good example of this.

When you give 1 < i < 10 to a C++ compiler, it is the same as:

Code:

---

(1 < i) < 10

---

So 1 < i is evaluated to a bool (true/false) and then that bool is tested on whether it is less than 10, which is always true, because true would be converted to 1 and false would be converted to 0, and both are less than 10. In other words, this is very bad because 1 < i < 10 is always true, even if i is 100.

ok another program I was working on......:confused:

Code:

---

#include <iostream>

/*  Write a program that will calculate the average of n data points which are entered by the
user and print out the average and the data points with the average subtracted. */

using namespace std;

  int main()
{
    int sum, i, datapts;
    double points [51];
    double mean;
    cout << "How numbers do you want to average? " << endl;
    cout << "(please enter more values then 2 but less then 50)" << endl;
    cin >> datapts;
            for (int i = 0; i < datapts; i++)
          {
            cout << "Enter number to average?" << endl;
            cin >> points[i];
          }
          if (datapts <= 1 || datapts >= 50)
            {
            cout << "Please enter correct amount to average between 2 to 50" << endl;
            return 0;
            }
    sum = sum + points [i];
    mean = sum / datapts;
    cout << "The average of your points are " << mean << endl;

    return 0;
}

---

I can't get it to work right. the program won't end if the amount of points is less the 1 or greater then 50 and the average is never right.:frown:

any help would be great
thanks:)

Code:

---

          if (datapts <= 1 || datapts >= 50)
            {
            cout << "Please enter correct amount to average between 2 to 50" << endl;
            return 0;
            }

---

Did you intend to check for incorrect amount of data points before trying to sample the data points?

Code:

---

    sum = sum + points [i];
    mean = sum / datapts;

---

Now, what the heck do you think this part of your code does?

Also, learn to indent properly.