cannot be used as a function error

Question

I am writing a simple program that uses functions found in different  cpp files  All of my prototypes are contained in a header file  I pass some of the functions into other functions and am not sure if I am doing it correctly  The error I get is   functionname  cannot be used as a function   The function it says cannot be used is the growthRate function and the estimatedPopulation function  The data comes in through an input function  which I do think is working    Thanks   header file    ifndef header h  define header h   include  lt iostream gt   include  lt iomanip gt   include  lt cstdlib gt    using namespace std     prototypes void extern input int amp   float amp   float amp   int amp    float extern growthRate  float  float   int extern estimatedPopulation  int  float   void extern output  int   void extern myLabel const char    const char       endif   growthRate function     include  header h   float growthRate  float birthRate  float deathRate  float growthrt                 growthrt     birthRate  -  deathRate       return growthrt         estimatedPopulation function        include  header h   int estimatedPopulation  int currentPopulation  float growthrt        return   currentPopulation     currentPopulation     growthrt   100       main    include  header h   int main          float birthRate  deathRate  growthRate      char response       int currentPopulation  years  estimatedPopulation       do   main loop                 input  currentPopulation  birthRate  deathRate  years           growthRate  birthRate  deathRate  growthrt            estimatedPopulation  currentPopulation  growthrt           output  estimatedPopulation  currentPopulation  growthrt            cout  lt  lt    n Would you like another population estimation   y n             cin  gt  gt  response                      while  response     Y     response     y         myLabel   5-19    12 09 2010            system   Pause         return 0

User · Answer

You can t pass a function as a parameter  Simply remove it from estimatedPopulation   and replace it with  float growthRate   use this in your calculation instead of calling the function   int estimatedPopulation  int currentPopulation  float growthRate        return  currentPopulation   currentPopulation   growthRate   100       and call it as   int foo   estimatedPopulation  currentPopulation  growthRate  birthRate  deathRate

User · Answer

Your compiler is right   You can t use the growthRate variable you declared in main as a function   Maybe you should pick different names for your variables so they don t override function names

User · Answer

include  header h   int estimatedPopulation  int currentPopulation  float growthRate        return currentPopulation   currentPopulation   growthRate    100

User · Answer

You are using growthRate both as a variable name and a function name  The variable hides the function  and then you are trying to use the variable as if it was the function - that is not valid   Rename the local variable

User · Answer

This line is the problem   int estimatedPopulation  int currentPopulation                           float growthRate  birthRate  deathRate     Make it   int estimatedPopulation  int currentPopulation  float birthRate  float deathRate    instead and invoke the function with three arguments like  estimatePopulation  currentPopulation  birthRate  deathRate      OR declare it with two arguments like   int estimatedPopulation  int currentPopulation  float growthrt             and call it as  estimatedPopulation  currentPopulation  growthRate  birthRate  deathRate      Edit   Probably more important here - C    and C  names have scope  You can have two things named the same but not at the same time  In your particular case your grouthRate variable in the main   hides the function with the same name  So within main   you can only access grouthRate as float  On the other hand  outside of the main   you can only access that name as a function  since that automatic variable is only visible within the scope of main     Just hope I didn t confuse you further

User · Answer

Modify your estimated population function to take a growth argument of type float   Then you can call the growthRate function with your birthRate and deathRate and use the return value as the input for grown into estimatedPopulation   float growthRate  float birthRate  float deathRate                 return   birthRate  -  deathRate           int estimatedPopulation  int currentPopulation  float growth        return   currentPopulation     currentPopulation     growth   100         main cpp int currentPopulation   100  int births   50  int deaths   25  int population   estimatedPopulation currentPopulation  growthRate births  deaths

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