Thread: Accessing Structs in Functions Problem

This C program is supposed to ask the user for the number of rows and columns, and output a rectangle of asterisks, like a visual times table. Not even getting to the output part yet, structs confuse the hell out of me, and when i try to compile, gcc gives these errors:

multiply.c:18: error: expected expression before box
multiply.c: In function draw_box:
multiply.c:51: error: incompatible type for argument 1 of draw_line
multiply.c:11: note: expected box but argument is of type int

really, using struct variables with functions is what's throwing me off

Code:

#include <stdio.h>

typedef struct {
int rows;
int columns;
} box;

int input_rows();
int input_columns();
void draw_box();
void draw_line(box data);

int main()
{
box data;
data.rows = input_rows();
data.columns = input_columns();
draw_box(box data);

return 0;
}

int input_rows(){

box data;

do{
printf ("Number of rows? \n");
scanf ("%d", &data.rows);
} while (data.rows <= 0);
return (data.rows);
}

int input_columns(){

box data;

do{
printf ("Number of columns? \n");
scanf ("%d", &data.columns);
} while (data.columns <= 0);
return (data.columns);
}

void draw_box(){

box data;
int x;
for(x=1;x<=data.rows;x++)
{
draw_line(data.columns);
}
}

void draw_line(box data){

int y;
for(y=1;y<=data.columns;y++);
{
printf("*");
}
}

You are calling it as draw_line(data.columns). data.columns is an int not a box, therefore the compiler is just noticing the obvious.

Also your draw_box function takes no arguments, yet you are passing it your box from main. You are then declaring a bogus local box in draw_box and are attempting to iterate to God knows where.

Code:

#include <stdio.h>

typedef struct {
  int rows;
  int columns;
} box;

int input_rows();
int input_columns();
void draw_box(); //!! you forgot to add the box parameter
void draw_line(box data);

int main()
{
  box data;
  data.rows = input_rows();
  data.columns = input_columns();
  draw_box(box data);  //!! delete the type, functions are called with variable names only

  return 0;
}

int input_rows(){

  box data;  // All you're interested in is an int, not a whole box

  do{
       printf ("Number of rows? \n");
       scanf ("%d", &data.rows);
   } while (data.rows <= 0);
  return (data.rows);
}

int input_columns(){

  box data; //!! ditto

  do{
       printf ("Number of columns? \n");
       scanf ("%d", &data.columns);
   }  while (data.columns <= 0);
  return (data.columns);
}

void draw_box(){

  box data;  //!! this box contains junk - it would be better with a parameter
  int x;
  for(x=1;x<=data.rows;x++)
  {
      draw_line(data.columns);
    }
}

void draw_line(box data){

  int y;
  for(y=1;y<=data.columns;y++);
  {
    printf("*");
  }
}

See the !! comments.

Looks, like the magic eye of Salem compiled it for you . Didn't notice all the other mistakes (actually the same mistake over and over).

Well yes, you need
int var;
scanf("%d",&var);
return var;
kinda thing.

post fixed (and thread close)