How to I return multiple values in a function
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Thread: How to I return multiple values in a function

  1. #1
    Join Date
    Apr 2010
    Posts
    5

    How to I return multiple values in a function

    OK, I a program that takes in data from a file and returns messages based upon it. Right now my function shot is supposed to be a multiple value returning function but I don't know how to return multiple values because it says that its not a void type variable. Any help on this would be great.


    Code:
    /Patrick Howard
    /*
    */
    //May 12, 2010
    #include <iostream>
    #include <iomanip>
    #include <string>
    #include <fstream>
    #include <cmath>
    // declared constants
    const float PI = 3.14159265f;
    const float NUM = 180.0f;
    const int AIRCRAFT_CARRIER = 3030; // targets locations in meters
    const int BATTLESHIP = 2000; // targets locations in meters
    const int DESTROYER = 1900; // targets locations in meters
    const int SUBMARINE = 1000; // targets locations in meters
    int  pv = 0;//public variable to test to see if it got hit or not
    int ahit = 6;
    int bhit = 5;
    int dhit = 3;
    int subhit = 2;
    using namespace std;
    // functions prototype
    float calcRadians(int deg);
    float fDistance(float , float vel);
    void shot(bool &isHit, float &distance);
    void print(string fileName, int falseData, int shots, int hits, int missed, int reload);
    int main()
    {
    	//declare number of hits for each ship
    	int aircraftHits = 6; // max number of hits for known targets
    	int battleshipHits = 5; // max number of hits for known targets
    	int destroyerHits = 3; // max number of hits for known targets
    	int submarineHits = 2; // max number of hits for known targets
    	int numShots = 0;
    	int numHits = 0;
    	int misses = 0;
    	int rounds = 0;
    	int amo = 2;
    	ifstream din;
    	string name;
    	bool hit = false;
    	bool badData = false;
    	int data = 0;
    	int degrees; // the angle in degrees
    	float velocity; // the initial velocity
    	float radians; // the radians
    	float distance; // the distance
    	do
    	{
    		cout << "Please enter the input file name. " << endl; // file name is entered
    		cin >> name; // name printed
    		din.open(name.c_str()); // file opened
    		if(!din.is_open()) // make sure file is real
    		{
    			cout << name << " is an invalid file name." <<endl; // if not found it will state that the file is invalid
    			din.clear();
    		}
    	}
    	while(!din.is_open());
    	{
    
    	while(din)
    	{
    		din >> degrees >> velocity; 
    		if(degrees <= 0 && velocity <= 0)
    		{
    			cout << "Bad data." << endl;
    			data ++;
    		}
    		else if(degrees <= 0)
    		{
    			cout << "Bad data." << endl;
    			data ++;
    		}
    		else if(velocity <= 0)
    		{
    			cout << "Bad data." << endl;
    			data ++;
    		}
    		else
    		{
    			din.ignore(80,'\n');
    			radians = calcRadians(degrees);
    			//cout << radians << endl;
    			distance = fDistance(velocity, radians);
    			//cout << distance << endl;
    			shot(hit, distance);
    			numShots++;
    			if(pv == 1)
    			numHits ++;
    			else
    			misses ++;
    			amo = amo - 1;
    			if(amo == 0)
    			{
    				rounds++;
    				amo = 2;
    			}
    			pv = 0;
    		}
    	}
    	}
    		print(name, badData, numShots, numHits, misses, rounds);//numhits6 misses2
    		return 0;
    }
    
    float calcRadians(int deg)
    {
    	float numerator;
    	float rad;
    	numerator = deg * PI;
    	rad = numerator / NUM;
    	//cout << rad << endl;
    	return rad;
    }
    
    float fDistance(float vel,float radians)
    {
    		float Distance;
    		Distance = (float)(((vel * vel)*(sin(2*radians))/32.2));
    		//cout << Distance << endl;
    		return Distance;
    }
    
    void shot(bool &isHit, float &distance)
    {
    		if(distance >= (AIRCRAFT_CARRIER - 1) && distance <= (AIRCRAFT_CARRIER + 1))
    		{
    		    isHit = true;
    			ahit = ahit - 1;
    			pv = 1;
    		}
    		else if (distance >= (-1 + BATTLESHIP) && distance <= (1 + BATTLESHIP))
    		{
    			isHit = true;
    			bhit = bhit - 1;
    			pv = 1;
    		}
    		else if(distance >= (-1 + DESTROYER) && distance <= (1 + DESTROYER))
    		{
    			isHit = true;
    			dhit = dhit - 1;
    			pv = 1;
    		}
    		else if(distance >= (-1 + SUBMARINE) && distance <= (1 + SUBMARINE))
    		{
    			isHit = true;
    			subhit = subhit - 1;
    			pv = 1;
    		}
    		return;
    }
    void print(string fileName, int falseData, int  reload, int hits, int missed)//num amo, num hits, num miss, percent, num of lines of bad data
    {
    		float percentage = 0;
    		ofstream dout;
    		cout << "Please enter the output file name. " << endl; 
    		cin >> fileName;
    		dout.open(fileName.c_str());
    		percentage = ((float)reload / hits);
    		dout << "The number rounds of ammo were expended: " << reload << endl;
    		dout << "The total number of hits overall: " << hits << endl;
    		dout << "The total number of misses were: " << missed << endl;
    		dout << "The percentage of hits to rounds expended: " << percentage << endl;
    		dout << "The number of lines of bad data in the file: " << falseData << endl;
    		dout.close();
    }

  2. #2
    Join Date
    Apr 1999
    Posts
    27,423

    Re: How to I return multiple values in a function

    Quote Originally Posted by patsies62 View Post
    OK, I a program that takes in data from a file and returns messages based upon it. Right now my function shot is supposed to be a multiple value returning function but I don't know how to return multiple values
    You cannot return multiple values in C++.

    Instead learn how to use structs or classes. Right now, your code has no use of these types. A struct/class holds multiple values, therefore if you return a single struct or class, you are returning "multiple values".

    Regards,

    Paul McKenzie

  3. #3
    Join Date
    Aug 2008
    Posts
    902

    Re: How to I return multiple values in a function

    If you only need to return two values, you can use a std:: pair.

  4. #4
    GCDEF is offline Elite Member Power Poster
    Join Date
    Nov 2003
    Posts
    12,055

    Re: How to I return multiple values in a function

    Another option is to use output parameters. Pass in parameters by reference and populate them inside the function.

  5. #5
    Join Date
    Nov 2001
    Posts
    244

    Re: How to I return multiple values in a function

    As Paul mentioned, structs is probably the easiest way.

    in header file:

    typedef struct tagMYSTRUCT {
    bool bHello;
    int nHello;
    CString csHello;
    } MYSTRUCT;


    in Source file

    MYSTRUCT MyFunction(int nParams)
    {
    MYSTRUCT myStruct;

    myStruct.bHello = true;
    myStruct.nHello = 512;
    myStruct.csHello.Format("Hi!");

    return myStruct;
    }

  6. #6
    Lindley is offline Elite Member Power Poster
    Join Date
    Oct 2007
    Location
    Fairfax, VA
    Posts
    10,888

    Re: How to I return multiple values in a function

    Quote Originally Posted by Anarchi View Post
    As Paul mentioned, structs is probably the easiest way.

    in header file:

    typedef struct tagMYSTRUCT {
    bool bHello;
    int nHello;
    CString csHello;
    } MYSTRUCT;


    in Source file

    MYSTRUCT MyFunction(int nParams)
    {
    MYSTRUCT myStruct;

    myStruct.bHello = true;
    myStruct.nHello = 512;
    myStruct.csHello.Format("Hi!");

    return myStruct;
    }
    I'd argue that ALLCAPSNAMES should be reserved for constants. Also, the "typedef struct" definition is unnecessary in C++ (though there is apparently a minor benefit to it, in that it will prevent accidental name hiding in a few rare cases).

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