Need Quick Help!!

AdamRA4 · #1 02-Dec-2005, 15:49

I have a program that I need to make and it has structs. I keep getting a 'illegal use of this type as an expression' error. Please help, any help is very appreciated!

CPP / C++ / C Code:


#include <iostream>
#include <cstdlib>

using namespace std;


struct Source
{
	float latitude1;
	float longitude1;
};
struct Travel
{
	float time;
	float distance;
	float altitude;
};
struct Target
{
	float latitude2;
	float longitude2;
};
struct Projectile
{
	float speed;
	float azimuthal;
	float equatorial;

	Source latitude1;
	Source longitude1;

	Travel time;
	Travel distance;
	Travel altitude;

	Target latitude2;
	Target longitude2;
};


//Projectile ReadEntry();
//int DisplayEntry (Projectile);


void main()
{

	cout << "Projectile Calculator\n\n";
	cout << "Please enter the launch speed: ";
    cin.getline(Projectile.speed,20);
	cout << endl;
//	cout << "\n\n" << Projectile.speed;
}

davekw7x · #2 02-Dec-2005, 16:04

Quote:

Originally Posted by AdamRA4

I have a program that I need to make and it has structs. I keep getting a 'illegal use of this type as an expression' error.

CPP / C++ / C Code:

void main()
{

	cout << "Projectile Calculator\n\n";
	cout << "Please enter the launch speed: ";
    cin.getline(Projectile.speed,20);
	cout << endl;
//	cout << "\n\n" << Projectile.speed;
}

The definition of Projectile tells the compiler that Projectile is a struct. You don't have any of them until your program declares variables of that type.
Once you declare a variable of type Projectile, then you can use access its members.

Also, since Projectile.speed is a float, you must have an input function that works with floats. cin.getline(...,...) works with strings, not floats.

You could try something the following main() function, based on your code, with your definitions. It's a start, I hope.

CPP / C++ / C Code:

int main()
{
    Projectile my_projectile;

    cout << "Projectile Calculator\n\n";
    cout << "Please enter the launch speed: ";

    cin >> my_projectile.speed;

    cout << "\n\nmy_projectile.speed = " << my_projectile.speed << endl;

    return 0;
}

Regards,

Dave

AdamRA4 · #3 02-Dec-2005, 16:09

Thanks, i will try it.

Thanks a million, that helped me out, I just couldnt decipher what it wanted me to do.

AdamRA4 · #4 02-Dec-2005, 16:14

instead of my_projectile I used projectileData.

so what if I wanted to cin a Travel distance, would it be

CPP / C++ / C Code:

projectileData.Travel.distance

??

AdamRA4 · #5 02-Dec-2005, 16:34

I am getting the same errors with the substructs, how do I do those?

CPP / C++ / C Code:

#include <iostream>
#include <cstdlib>
#include <cmath>

using namespace std;


struct Source
{
	float latitude1;
	float longitude1;
};
struct Travel
{
	float time;
	float distance;
	float altitude;
};
struct Target
{
	float latitude2;
	float longitude2;
};
struct Projectile
{
	float speed;
	float azimuthal;
	float equatorial;

	Source latitude1;
	Source longitude1;

	Travel time;
	Travel distance;
	Travel altitude;

	Target latitude2;
	Target longitude2;
};



bool GetFloat(float *);
bool validNum = true;


void main()
{
	Projectile projectileData;

	cout << "Projectile Calculator\n\n";
	cout << "Please enter the launch speed: ";
	validNum = GetFloat(&projectileData.speed);
//	cin >> projectileData.speed;
	cout << endl;

	cout << "Please enter the launch azimuthal angle: ";
    cin >> projectileData.azimuthal;
	cout << endl;

	cout << "Please enter the launch equatorial angle: ";
    cin >> projectileData.equatorial;
	cout << endl;

	cout << "Please enter the source latitude: ";
    cin >> projectileData.Source.latitude1;
	cout << endl;

	cout << "Please enter the source longitude: ";
    cin >> projectileData.longitude1;
	cout << endl;



	projectileData.time = 2.0*projectileData.speed*sin(projectileData.azimuthal)/9.81;

	projectileData.distance = projectileData.speed*cos(projectileData.azimuthal)*projectileData.time;

	projectileData.altitude = 9.81*projectileData.time*projectileData.time/2.0;

	projectileData.latitude2 = projectileData.latitude1 + projectileData.distance*sin(projectileData.equatorial);

	projectileData.longitude2 = projectileData.longitude1 + projectileData.distance*cos(projectileData.equatorial);


	cout << "The projectile is launched with a speed of: " << projectileData.speed << endl;
	cout << "                     an azimuthal angle of: " << projectileData.azimuthal << endl;
	cout << "                     an equtorial angle of: " << projectileData.equatorial << endl;
	cout << "          The projectile travels a time of: " << Projectile.time << endl;
	cout << "                        over a distance of: " << Projectile.distance << endl;
	cout << "                    reaches an altitude of: " << Projectile.altitude << endl;
	cout << "               It departs from coordinates: " << Projectile.latitude1 << ", " << Projectile.longitude1 << endl;
	cout << "                and arrives at coordinates: " << Projectile.latitude2 << ", " << Projectile.longitude2 << endl;



}


bool GetFloat(float *value)
{
	char string[20];
	bool validNum = true;
	int i;

	cin >> projectileData.speed;

//	cin.getline(string,20);

	i = 0;
	do
	{
		if ((string[i] < '0') || (string[i] > '9'))
		{
			validNum = false;
		}
		i++;
	} while (i < strlen(string) && validNum);

	if (validNum)
	{
		*value = atoi(string);
	}

	return validNum;
}


void DisplayEntry(Projectile)
{
	cout << "The projectile is launched with a speed of: " << Projectile.speed << endl;
	cout << "                     an azimuthal angle of: " << Projectile.azimuthal << endl;
	cout << "                     an equtorial angle of: " << Projectile.equatorial << endl;
	cout << "          The projectile travels a time of: " << Projectile.speed << endl;
	cout << "                        over a distance of: " << Projectile.time << endl;
	cout << "                    reaches an altitude of: " << Projectile.altitude << endl;
	cout << "               It departs from coordinates: " << Projectile.latitude1 << ", " << Projectile.longitude1 << endl;
	cout << "                and arrives at coordinates: " << Projectile.latitude2 << ", " << Projectile.longitude2 << endl;
}

AdamRA4 · #6 02-Dec-2005, 16:49

Also I just noticed that my DisplayEntry was their twice, I deleted the entries from the main() function.

AdamRA4 · #7 02-Dec-2005, 17:13

Updated my code, I only get about 18 errors, most of which are the 'illegal use of this type as an expression' error with the SubStructs. This is an assignment which I have to turn-in in about 10 min. If I could figure out how to get rid of the 'illegal use of this type as an expression' errors, I would help greatly.

CPP / C++ / C Code:

#include <iostream>
#include <cstdlib>
#include <cmath>

using namespace std;


struct Source
{
	float latitude1;
	float longitude1;
};
struct Travel
{
	float time;
	float distance;
	float altitude;
};
struct Target
{
	float latitude2;
	float longitude2;
};
struct Projectile
{
	float speed;
	float azimuthal;
	float equatorial;

	Source latitude1;
	Source longitude1;

	Travel time;
	Travel distance;
	Travel altitude;

	Target latitude2;
	Target longitude2;
};



bool GetFloat(float *);
bool validNum = true;
Projectile projectileData;

void main()
{
	cout << "Projectile Calculator\n\n";

	do  //reads the Projectile Speed
	{
		cout << "Please enter the launch speed: ";
		validNum = GetFloat(&projectileData.speed);
		if (validNum==false)
		{
			cout << "Invalid number. Try again...\n";
		}
	} while (validNum==false);


	cout << "Please enter the launch speed: ";
	validNum = GetFloat(&projectileData.speed);
	cout << endl;

	cout << "Please enter the launch azimuthal angle: ";  //reads the Projectile azimuthal angle
    cin >> projectileData.azimuthal;
	cout << endl;

	cout << "Please enter the launch equatorial angle: ";  //reads the Projectile equatorial angle
    cin >> projectileData.equatorial;
	cout << endl;

	cout << "Please enter the source latitude: ";  //reads the Projectile source latitude
    cin >> projectileData.latitude1;
	cout << endl;

	cout << "Please enter the source longitude: ";  //reads the Projectile source longitude
    cin >> projectileData.longitude1;
	cout << endl;



	projectileData.time = 2.0*projectileData.speed*sin(projectileData.azimuthal)/9.81;  //calculation for Projectile time

	projectileData.distance = projectileData.speed*cos(projectileData.azimuthal)*projectileData.time;  //calculation for Projectile distance

	projectileData.altitude = 9.81*projectileData.time*projectileData.time/2.0;  //calculation for Projectile altitude

	projectileData.latitude2 = projectileData.latitude1 + projectileData.distance*sin(projectileData.equatorial);  //calculation for Projectile target latitude

	projectileData.longitude2 = projectileData.longitude1 + projectileData.distance*cos(projectileData.equatorial);  //calculation for Projectile target longitude


}


bool GetFloat(float *value)
{
	char string[20];
	bool validNum = true;
	int i;

	cin >> projectileData.speed;

	i = 0;
	do
	{
		if ((string[i] < '0') || (string[i] > '9'))
		{
			validNum = false;
		}
		i++;
	} while (i < strlen(string) && validNum);

	if (validNum)
	{
		validNum  = true;
	}

	return validNum;
}


void DisplayEntry(Projectile)  //Display's the final results of the calculations and such
{
	cout << "The projectile is launched with a speed of: " << Projectile.speed << endl;
	cout << "                     an azimuthal angle of: " << Projectile.azimuthal << endl;
	cout << "                     an equtorial angle of: " << Projectile.equatorial << endl;
	cout << "          The projectile travels a time of: " << Projectile.speed << endl;
	cout << "                        over a distance of: " << Projectile.time << endl;
	cout << "                    reaches an altitude of: " << Projectile.altitude << endl;
	cout << "               It departs from coordinates: " << Projectile.latitude1 << ", " << Projectile.longitude1 << endl;
	cout << "                and arrives at coordinates: " << Projectile.latitude2 << ", " << Projectile.longitude2 << endl;
}

Paramesh · #8 02-Dec-2005, 19:29

Hi Adam,

First, Change the Source definition like this:

CPP / C++ / C Code:

struct Position
{
    float latitude;
    float longitude;
};

Change the name to position because we can use position to indicate both source and target.

Remove the target struct definition.

Then, change the projectile definition like this:

CPP / C++ / C Code:

struct Projectile
{
    float speed;
    float azimuthal;
    float equatorial;

    Position Source;   // Source is a position
    Position Target;   // Target is a position

    Travel Path;
};

Here are the variables that you should use in your functions:

Code:

projectileData.speed
projectileData.azimuthal
projectileData.equatorial
projectileData.Source.latitude
projectileData.Source.longitude
projectileData.Target.latitude
projectileData.Target.longitude
projectileData.Path.time
projectileData.Path.distance
projectileData.Path.altitude

Regards,

Paramesh.

AdamRA4 · #9 04-Dec-2005, 00:23

thanks, I will try that

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