1 files changed, 221 insertions, 0 deletions
diff --git a/challenge-165/duncan-c-white/C/ch-2.c b/challenge-165/duncan-c-white/C/ch-2.c
new file mode 100644
index 0000000000..7a71c5f957
--- /dev/null
+++ b/challenge-165/duncan-c-white/C/ch-2.c
@@ -0,0 +1,221 @@
+/*
+ * Task 2: Line of Best Fit
+ * 
+ * GUEST LANGUAGE: This is my attempt to translate ch-2.pl into C
+ */ 
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+#include <ctype.h>
+#include <assert.h>
+
+#include "MySVG.h"
+
+bool debug=0;
+
+// char *s = process_singlearg( argc, argv );
+//	Process the -d flag, and check that there is a single
+//	remaining argument, return it
+char * process_singlearg( int argc, char **argv )
+{
+	int arg=1;
+	if( argc>1 && strcmp( argv[arg], "-d" ) == 0 )
+	{
+		debug = true;
+		arg++;
+	}
+
+	int left = argc-arg;
+	if( left != 1 )
+	{
+		fprintf( stderr,
+			"Usage: best-fit [-d] filename\n" );
+		exit(1);
+	}
+
+	// element is in argv[arg]
+
+	if( debug )
+	{
+		printf( "debug: remaining argument is in pos %d, and is %s\n",
+			arg, argv[arg] );
+	}
+
+	return argv[arg];
+}
+
+
+typedef struct { int x, y; } datapoint;
+typedef struct { int x1, y1, x2, y2; } dataline;
+
+#define MAXITEMS 1024
+
+int npoints = 0;
+datapoint pt[MAXITEMS]; 	// input points
+
+datapoint wh;		// wh.x == width of our data, wh.y == height of our data
+
+
+/*
+ * updatewh( x, y );
+ *	Update wh to include x and y.
+ */
+void updatewh( int x, int y )
+{
+	assert( x>=0 );
+	assert( y>=0 );
+	if( x > wh.x ) wh.x = x;
+	if( y > wh.y ) wh.y = y;
+}
+
+
+/*
+ * bool lineread = readline( in, buf, maxlen );
+ *      read a single line from in (a FILE * open for input)
+ *      into a character buffer (char *), reading no more than
+ *      maxlen characters, removing a trailing '\n' from the
+ *      buffer (if there is one).
+ *
+ *      If the input line is longer than that, the REMAINDER OF
+ *      THE LINE IS LEFT IN the file's input buffer for later reading.
+ *      If readline() is called again immediately, the remainder of
+ *      the line will be treated as a separate line.
+ *
+ *      In caller-space, buf must be a writable character buffer of
+ *      size >= maxlen, i.e. typically either a char [n]
+ *      or a malloc(n * sizeof(char)) chunk,
+ *      where (in both cases) n >= maxlen
+ */
+bool readline( FILE *in, char *buf, int maxlen )
+{
+        if( fgets( buf, maxlen, in ) == 0 )
+        {
+                return false;
+        }
+        int l = strlen(buf);
+        if( l>0 && buf[l-1]=='\n' )
+        {
+                buf[l-1] = '\0';
+        }
+        return true;
+}
+
+
+/*
+ *
+ * read_data( in );
+ *	Read data (points) from in.
+ */
+void read_data( FILE *in )
+{
+	#define MAXLINELEN 100
+	char line[MAXLINELEN];
+
+	npoints = 0;
+	while( readline(in, line, MAXLINELEN ) )
+	{
+		int x, y;
+		char *s;
+		char *p;
+
+		s = line;
+		assert( isdigit(*s) );
+		p = strchr(s,',');
+		assert( p != NULL );
+		*p = '\0';
+		x = atoi(s);
+
+		s = p+1;
+		assert( isdigit(*s) );
+		y = atoi(s);
+
+		//fprintf( stderr, "debug: read point %d,%d\n", x, y );
+		pt[npoints].x = x;
+		pt[npoints].y = y;
+		npoints++;
+		updatewh( x, y );
+	}
+}
+
+
+/*
+ * bestfit( points, npoints, &m, &c );
+ *	Calculate y=mx+c, the best fit line of the data (each data point an [x,y] pair)
+ */
+void bestfit( datapoint *pt, int npoints, double *m, double *c )
+{
+	int sumx = 0;
+	int sumy = 0;
+	int sumxy = 0;
+	int sumx2 = 0;
+	for( int i=0; i<npoints; i++ )
+	{
+		int x = pt[i].x;
+		int y = pt[i].y;
+		sumx += x;
+		sumy += y;
+		sumxy += x * y;
+		sumx2 += x * x;
+	}
+
+	*m = (npoints * sumxy - sumx * sumy) / (double) (npoints * sumx2 - sumx * sumx);
+	*c = (sumy - *m * sumx) / (double)npoints;
+
+	if( debug )
+	{
+		fprintf( stderr, "bestfit: n=%d, sumx=%d, sumy=%d, sumxy=%d, sumx^2=%d\n",
+			npoints, sumx, sumy, sumxy, sumx2 );
+		fprintf( stderr, "bestfit: m=%.6f, c=%.6f\n", *m, *c );
+	}
+}
+
+
+int main( int argc, char **argv )
+{
+	char *filename = process_singlearg( argc, argv );
+
+	wh.x = -1;
+	wh.y = -1;
+
+	FILE *in = fopen( filename, "r" );
+	assert( in != NULL );
+	read_data( in );
+	fclose( in );
+
+	int w = wh.x;
+	int h = wh.y;
+
+	w += (10-w%10);
+	h += (10-h%10);
+
+	int xscale = w < 200 ? 200/w : 1;
+	int yscale = h < 200 ? 200/h : 1;
+
+	if( debug )
+	{
+		fprintf( stderr, "maxxy rectangle is w %d, h %d, xscale %d, yscale %d\n", w, h, xscale, yscale );
+	}
+
+	double m, c;
+	bestfit( pt, npoints, &m, &c );
+	int y1 = (int) (m + c);			// for x==1
+	int y2 = (int) (m * (w-1) + c);		// for x==w-1
+
+	start_svg( w * xscale, h * yscale );
+
+	setcolour( "blue" );
+	setlinewidth( 1 );
+	line( 1, y1*yscale, (w-1)*xscale, y2*yscale );
+
+	setcolour( "orange" );
+	for( int i=0; i<npoints; i++ )
+	{
+		point( pt[i].x*xscale, pt[i].y*yscale );
+	}
+
+	end_svg();
+
+	return 0;
+}