Thread: writing a pair of numbers to an array

Heres what I have after all your wonderful advice. Everythings works awesome, thanks everyone, time to move on to sorting and all that fun stuff

Code:

#include <stdio.h>

//function prototype
void read_location(double *x, double *y);

//main program
int main ()
{
	struct coord{
		double x;
		double y;
	};
	
	struct coord array[20];

	int index=0;
	do
	{
		read_location( &array[index].x, &array[index].y);
		index++;
	}while(index < 5);
	
	printf("%lf", array[3].x);
	return 0;
	}

void read_location(double *x, double *y)
{
	printf("Enter x:\n");
	scanf("%lf", x);
	printf("Enter y:\n");
	scanf("%lf", y);
}

Originally Posted by Adak

I'll be back, shortly.

What compiler are you using?

Change %d in printf() to a double format.

your void function should be void, so remove the int return type. Add a prototype for the function, above main().

I've got to look up something about doubles, grrrrr!

Im using a gcc compiler on linux. Could you explain the whole void instead of int thing? Im not finding the info I need on google. They both seem to work fine in this code, is there any advantage to using void?

void return type just means there is no return from that function.

C (especially older compilers), assume that any function with no prototype, will have an int return type.

Then when there is no return in the function, the compiler should give you an error message.

This is my take on your program:

Code:

#include <stdio.h>
#include <math.h>

//don't call this - just forces floating point formats to link in 
//my old Borland Turbo C/C++
static void forcefloat(float *p)
{ float f = *p;
  forcefloat(&f);
}

//The is is the function prototype - you should always use them.
//It's just the first line of the function, put before main();
void read_location(double *x, double *y);

struct coord{
	double x;
	double y;
};

struct coord array[20];

int main ()
{
   int index=0, i;
   putchar('\n');
   do
	{
		read_location( &array[index].x, &array[index].y);
		index++;
	}while(index < 5);
	
   for(i = 0; i < 5; i++)
	   printf("\n%d: x = %6lf, y = %6lf", i, array[i].x, array[i].y);

   printf("\n\n\t\t\t     Press Enter When Ready ");
   while((i = getchar()) != '\n' );
   i = getchar();
	return 0;
}

void read_location(double *x, double *y) 
{

	printf("Enter x:\n");
	scanf(" %lf", x);
	printf("Enter y:\n");
	scanf(" %lf", y);
}

Glad you got it working. Well done!

Thanks Adak, I couldnt have done it without you guys I have one very last question. I wrote a sorting program that will sort the x's and y's in ascending order:

Code:

int pass;
int a;
int hold;

for(pass=1; pass< index; pass++)
{
	for (a=0; a < index -1; a++)
	{
		if (array[a].x > array[a+1].x)
		{
			hold=array[a].x;
			array[a].x = array[a+1].x;
			array[a+1].x=hold;
		}
	}
}

printf("ordered x's:\n");
for (a=0; a< index; a++)
	{
		printf("%4lf", array[a]);
	}

This kind of goes back to one of my original question, how do I display the ys that were paired with the x's?

Oh you can't just swap the x's. That's the whole point. Swap the entire struct.

Originally Posted by tabstop

Oh you can't just swap the x's. That's the whole point. Swap the entire struct.

My issue is that I will have to sort them by the y's as well. So if I swap the entire struct, will i still be able to sort the y's later on? And to swap the struct, i just remove the ".x" right?

Of course.

Your hold variable has to be changed to a struct, however. An int won't do.

Originally Posted by tabstop

Of course.

Im getting this error when I remove the ".x"

[CODEgps.c: In function ‘main’:
grid.c:61: error: invalid operands to binary > (have ‘struct coord’ and ‘struct coord’)
grid.c:63: error: incompatible types when assigning to type ‘int’ from type ‘struct coord’
grid.c:65: error: incompatible types when assigning to type ‘struct coord’ from type ‘int’][/CODE]

You can't remove it from the check, just from the swap.

Originally Posted by tabstop

You can't remove it from the check, just from the swap.

Im still getting errors for the swap part:

Code:

			hold=array[a];
			array[a] = array[a+1];
			array[a+1]=hold;

Did you change hold to be a struct instead of just an int?

Originally Posted by Adak

Did you change hold to be a struct instead of just an int?

Im assuming this isnt as easy as just writing "struct hold;"?

Your struct has a name that defines it's contents. Use struct and then the name of the type of struct, and then hold.

Try that!