diff --git a/AUTHORS b/AUTHORS
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diff --git a/CHANGELOG b/CHANGELOG
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diff --git a/COPYING b/COPYING
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diff --git a/README b/README
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diff --git a/SAMPLE_PROGRAMS b/SAMPLE_PROGRAMS
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diff --git a/src/keyboard.c b/src/keyboard.c
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diff --git a/src/keyboard.h b/src/keyboard.h
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diff --git a/src/m6502.c b/src/m6502.c
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diff --git a/src/m6502.h b/src/m6502.h
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diff --git a/src/main.c b/src/main.c
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diff --git a/src/makefile b/src/makefile
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diff --git a/src/memory.c b/src/memory.c
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diff --git a/src/memory.h b/src/memory.h
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diff --git a/src/msgbuf.c b/src/msgbuf.c
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diff --git a/src/msgbuf.h b/src/msgbuf.h
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diff --git a/src/pia6820.c b/src/pia6820.c
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diff --git a/src/pia6820.h b/src/pia6820.h
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diff --git a/src/screen.c b/src/screen.c
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index 629acbc..3113604
--- a/src/screen.c
+++ b/src/screen.c
@@ -36,6 +36,8 @@ static int indexX, indexY;
 static WINDOW *screen;
 static long long interval_start; /* interval start time in u sec */
 
+int nrow, ncol;
+
 char getch_screen(void)
 {
 	return (char)wgetch(screen);
diff --git a/src/screen.h b/src/screen.h
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index 88bdbb3..3324fad
--- a/src/screen.h
+++ b/src/screen.h
@@ -25,5 +25,5 @@ void outputDsp(unsigned char dsp);
 char getch_screen(void);
 void select_screen(void);
 
-int nrow, ncol;
+extern int nrow, ncol;