C program function error - c

Question

This code has to get coordinates and write them to the coords array, and also return the number of coordinates that have been entered.
The code has to stop once the user enters 0 0 but the code should not save it.
For example if I enter 1 2 3 4 0 0 the code will set the array to (1,2) (3,4).
But in this code when I enter 0 0 it show me error, and once I enter the numbers at first the print show me just zeros.
int coordinatesread(double coords[][DIM], int n)
{
double columnin, rowin;
int row=0;
while(row!=n-1)
{
scanf ("%lf",&columnin);
scanf ("%lf",&rowin);
if (columnin==0 && rowin==0)
{
return row+1;
}
else
{
coords[row][0]=columnin;
coords[row][1]=rowin;
++row;
}
printf("%.3lf %.3lf", coords[row][0], coords[row][1]); /* TEST */
}
return row+1;
}

Answer 1

The problem is that when you print coords[row][0] and coords[row][1] you are actually sending to stdout the next coordinates which are not still entered by the user. You are sending to stdout undefined values and not the values you entered. The line printf("%.3lf %.3lf", coords[row][0], coords[row][1]); should be printf("%.3lf %.3lf\n", coords[row-1][0], coords[row-1][1]); And add the next to line \n otherwise the information printed is illisible.
Try this code
#include <stdio.h>
#include <stdlib.h>
#define DIM 2
int coordinatesread(double coords[][DIM], int n)
{
double columnin, rowin;
int row=0;
while(row!=n-1)
{
scanf ("%lf",&columnin);
scanf ("%lf",&rowin);
if (columnin==0 && rowin==0)
{
return row+1;
}
else
{
coords[row][0]=columnin;
coords[row][1]=rowin;
row++;
}
printf("%.3lf %.3lf\n", coords[row-1][0], coords[row-1][1]); /* TEST */
}
return row+1;
}
int main(void)
{
double cords[5][2];
int n = 5;
coordinatesread(cords, n);
return 0;
}

Answer 2

Okey, let's see. The problem in your code is that you are incrementing the value of row before printing the values in coords[row][0]=columnin
You are not going to print a line if the values are both zero, so you can move this line:
printf("%.3lf %.3lf", coords[row][0], coords[row][1]);
Right before this one:
++row;
The new code should look like this:
int coordinatesread(double coords[][DIM], int n)
{
double columnin, rowin;
int row=0;
while(row!=n-1)
{
scanf ("%lf",&columnin);
scanf ("%lf",&rowin);
if (columnin==0 && rowin==0)
{
return row+1;
}
else
{
coords[row][0]=columnin;
coords[row][1]=rowin;
printf("%.3lf %.3lf", coords[row][0], coords[row][1]);
++row;
}
}
return row+1;
}
PD:
Notice that your code does not work fine if you want to scan N valid coordinates, because the last one will be ignored. The problem is here:
while(row!=n-1)
If you have decided to use while loop instead of for, you should iterate until row = N. Let's suppose N = 3. If you want to scan 3 valid coordinates, the loop will iterate while N != 2. This will scan only two of them (when row = 0 and row = 1). Change it to:
while(row!=n)
In addition, when you are iterating over an array (or a table in this case), using for is better than while. Both are correct, but for is more stylized. If you change it, the code look like this:
int coordinatesread(double coords[][DIM], int n)
{
double columnin, rowin;
for(int row = 0; i < n; i++)
{
scanf ("%lf",&columnin);
scanf ("%lf",&rowin);
if (columnin==0 && rowin==0)
{
return row+1;
}
else
{
coords[row][0]=columnin;
coords[row][1]=rowin;
printf("%.3lf %.3lf", coords[row][0], coords[row][1]);
}
}
return row;
}