Thread: calculate a rectangle's area

I am writing a program to calculate a rectangle's area.

Eg.
Enter top left point: 1 1 (User input)
Enter bottom right point: 2 -1 (User input)
Top Left x = 1.000000 y: 1.000000
Bottom Right x = 2.000000 y: -1.000000
Area = 2.000000 (Program output)



It keeps on prompting me my variable r is being used without being initialized, when I think I already did so.

Code:

typedef struct { 
	double x; 
	double y; 
} Point; 


typedef struct { 
	Point topLeft; /* top left point of rectangle */ 
	Point botRight; /* bottom right point of rectangle */ 
} Rectangle; 


Point p;
Rectangle r;


printf("Enter top left point : ");
scanf("\n%f",r.topLeft);
printf("\n%f",r.topLeft);


printf("Enter bottom right point : ");
scanf("\n%f", r.botRight);
printf("\n%f",r.botRight);


computeArea(&r);
printf("\n%rectangle",r);



double computeArea(Rectangle *r)
{ 
	double h=0,w=0;


	w=fabs(r->botRight.x - r->topLeft.x);
	h=fabs(r->topLeft.y - r->botRight.y);


	return (w*h);
}

Please post the complete error messages, exactly as they appear in your development environment.

And again I think you should review the documentation for the scanf() function.

Jim

It gives me this error message:



This scanf is to retrieve integer data the user keyed in. Other than scanf to retrieve what user keyed in, may I what else I can use? Eg. for retrieving char, we can use getchar(), what about for integer case?

You need to pass a pointer to scanf, not the variable itself, then code compiles no problem for me (Code:Blocks on Win7). However, no matter what I input, printf always writes 0.00000. So it seems there's more than wrong.

Look closely at one of your scanf() calls.

Code:

scanf("\n%f",r.topLeft);

There are several things wrong with this scanf(). First that extra character in your specifier string ( '\n' ) is going to cause problems, get rid of it.

Next as I said earlier you need to find and read the documentation for scanf(). The format specifiers must exactly match the variable, your's don't match. What is the format specifier for a double?

Next topLeft is a structure. What variable are you actually trying to get with this scanf()?

Lastly you need to find and read the documentation for scanf(). This function expects an address of a variable. Are you doing that? Answer = NO!.

Jim