foo was not declared in this scope c

Question

I m just learning c    first day looking at it since I took a 1 week summer camp years ago   I was converting a program I m working on in Java to C      ifndef ADD H  define ADD H  define  USE MATH DEFINES  include  lt iostream gt   include  lt math h gt   using namespace std   class Evaluatable   public    virtual double evaluate double x       class SkewNormalEvalutatable   Evaluatable  public    SkewNormalEvalutatable      double evaluate double x       return 1   sqrt 2   M PI    pow 2 71828182845904523536  -x   x   2           SkewNormalEvalutatable  SkewNormalEvalutatable        double getSkewNormal double skewValue  double x      SkewNormalEvalutatable e       return 2   sqrt 2   M PI    pow 2 71828182845904523536  -x   x   2    integrate -1000  skewValue   x  10000  e         double normalDist double x        return 1   Math sqrt 2   Math PI    Math pow Math E  -x   x   2         double integrate  double start  double stop                                       int numSteps                                        Evaluatable evalObj      double stepSize    stop - start     double numSteps    start   start   stepSize   2 0    return  stepSize   sum start  stop  stepSize  evalObj       double sum  double start  double stop                                 double stepSize                                 Evaluatable evalObj      double sum   0 0  current   start    while  current  lt   stop        sum    evalObj evaluate current       current    stepSize        return sum         int main             cout  lt  lt  getSkewNormal 10 0  0   lt  lt  endl       return 0        endif   The errors were   SkewNormal h  In function  double getSkewNormal double  double     SkewNormal h  29  error   integrate  was not declared in this scope SkewNormal h  In function  double integrate double  double  int  Evaluatable    SkewNormal h 41  error   sum  was not declared in this scope   Integrate and sum are both supposed to be functions  Here is the Java code  more or less the same   public static double negativelySkewed double skew  int min  int max       return randomSkew skew     max - min    min     public static double randomSkew final double skew       final double xVal   Math random        return 2   normalDist xVal    Integral integrate -500  skew   xVal  100000  new Evaluatable               Override         public double evaluate double value                return normalDist value                        public static double normalDist double x       return 1   Math sqrt 2   Math PI    Math pow Math E  -x   x   2          A class to calculate summations and numeric integrals  The     integral is calculated according to the midpoint rule         Taken from Core Web Programming from      Prentice Hall and Sun Microsystems Press      http   www corewebprogramming com        amp copy  2001 Marty Hall and Larry Brown      may be freely used or adapted        public static class Integral         Returns the sum of f x  from x start to x stop  where the       function f is defined by the evaluate method of the        Evaluatable object           public static double sum double start  double stop                             double stepSize                             Evaluatable evalObj        double sum   0 0  current   start      while  current  lt   stop          sum    evalObj evaluate current         current    stepSize            return sum              Returns an approximation of the integral of f x  from        start to stop  using the midpoint rule  The function f is       defined by the evaluate method of the Evaluatable object           public static double integrate double start  double stop                                   int numSteps                                    Evaluatable evalObj        double stepSize    stop - start     double numSteps      start   start   stepSize   2 0      return stepSize   sum start  stop  stepSize  evalObj               An interface for evaluating functions y   f x  at a specific     value  Both x and y are double-precision floating-point      numbers         Taken from Core Web Programming from      Prentice Hall and Sun Microsystems Press      http   www corewebprogramming com        amp copy  2001 Marty Hall and Larry Brown      may be freely used or adapted       public static interface Evaluatable         public double evaluate double value       I m certain it s something very simple  Also  how do I call  getSkewNormal double skewValue  double x    From a file outside SkewNormal h

User · Answer

In general  in C   functions have to be declared before you call them  So sometime before the definition of getSkewNormal    the compiler needs to see the declaration   double integrate  double start  double stop  int numSteps  Evaluatable evalObj     Mostly what people do is put all the declarations  only  in the header file  and put the actual code -- the definitions of the functions and methods -- into a separate source    cc or   cpp  file  This neatly solves the problem of needing all the functions to be declared

User · Answer

In C    your source files are usually parsed from top to bottom in a single pass  so any variable or function must be declared before they can be used  There are some exceptions to this  like when defining functions inline in a class definition  but that s not the case for your code   Either move the definition of integrate above the one for getSkewNormal  or add a forward declaration above getSkewNormal   double integrate  double start  double stop  int numSteps  Evaluatable evalObj     The same applies for sum

User · Answer

In C   you are supposed to declare functions before you can use them  In your code integrate is not declared before the point of the first call to integrate  The same applies to sum  Hence the error  Either reorder your definitions so that function definition precedes the first call to that function  or introduce a  forward  non-defining declaration for each function   Additionally  defining external non-inline functions in header files in a no-no in C    Your definitions of SkewNormalEvalutatable  SkewNormalEvalutatable  getSkewNormal  integrate etc  have no business being in header file   Also SkewNormalEvalutatable e    declaration in C   declares a function e  not an object e as you seem to assume  The simple SkewNormalEvalutatable e  will declare an object initialized by default constructor   Also  you receive the last parameter of integrate  and of sum  by value as an object of Evaluatable type  That means that attempting to pass SkewNormalEvalutatable as last argument of integrate will result in SkewNormalEvalutatable getting sliced to Evaluatable  Polymorphism won t work because of that  If you want polymorphic behavior  you have to receive this parameter by reference or by pointer  but not by value

[c++] 'foo' was not declared in this scope c++

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