From ad31ff953bde645086a2a35b058524b7002ff2b1 Mon Sep 17 00:00:00 2001
From: zlg <zlg@zlg.space>
Date: Wed, 6 Feb 2013 01:23:47 -0600
Subject: First crack at 1-24

Committing before I try something different.
---
 1-24_syntax-checker.c | 151 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 151 insertions(+)
 create mode 100644 1-24_syntax-checker.c

(limited to '1-24_syntax-checker.c')

diff --git a/1-24_syntax-checker.c b/1-24_syntax-checker.c
new file mode 100644
index 0000000..f56e4f7
--- /dev/null
+++ b/1-24_syntax-checker.c
@@ -0,0 +1,151 @@
+#include <stdio.h>
+
+/* The C Programming Language: 2nd Edition
+ * Exercise 1-24:
+ * "Write a program to check a C program for rudimentary syntax errors like
+ * unbalanced parentheses, brackets, and braces. Don't forget about quotes, both
+ * single and double, escape sequences, and comments. (This program is hard if
+ * you do it in full generality.)"
+ *
+ * Proksima from Freenode's ##c helped me understand full generality where
+ * Ixquick, Wikipedia, and StackOverflow all failed: a program that has full
+ * generality handles all use cases. In this case, my program should report no
+ * errors from a well formed C source file, and return correct errors for every
+ * non-valid C source file.
+ *
+ * I can tackle this one the same way I tackled the previous exercise: with a
+ * FSM. The trick is in catching the mismatched levels.
+ */
+
+/* Create our nestable counts. These keep track of each type of syntax
+ * character. */
+#define PARENS 0
+#define BRACKETS 1
+#define BRACES 2
+
+/* Create our states, which tell the parser what's going on. INSQ, INDQ, and
+ * INCM are much larger so it's easier to tell what's what. If I were better
+ * versed in binary operations, this could use less RAM. I intend to revisit
+ * this later on. */
+#define OUT 0
+#define INPR 1
+#define INBK 2
+#define INBC 3
+#define INSQ 100
+#define INDQ 1000
+#define INCM 10000
+
+char c;
+int counts[3];
+int state, i, linenr;
+
+int main() {
+	for (i = 0; i < 3; ++i) {
+		counts[i] = 0;
+	}
+
+	state = OUT;
+	linenr = 1;
+	// Begin streaming!
+	while ((c = getchar()) != EOF) {
+		if (c == '\n') {
+			linenr += 1;
+			if (state >= INSQ) {
+				break;
+			}
+		}
+		if (c == '(') {
+			counts[PARENS] += 1;
+			state += INPR;
+		}
+		if (c == ')') {
+			counts[PARENS] -= 1;
+			state -= INPR;
+			if (counts[PARENS] < 0) {
+				break;
+			}
+		}
+		if (c == '[') {
+			counts[BRACKETS] += 1;
+			state += INBK;
+		}
+		if (c == ']') {
+			counts[BRACKETS] -= 1;
+			state -= INBK;
+			if (counts[BRACKETS] < 0) {
+				break;
+			}
+		}
+		if (c == '{') {
+			counts[BRACES] += 1;
+			state += INBC;
+		}
+		if (c == '}') {
+			counts[BRACES] -= 1;
+			state -= INBC;
+			if (counts[BRACES] < 0) {
+				break;
+			}
+		}
+		if (c == '"' && state > INDQ) {
+			state -= INDQ;
+			if (state < 0) {
+				break;
+			}
+		}
+		if (c == '"' && state < INSQ) {
+			state += INDQ;
+			if (state >= (INDQ * 2)) {
+				break;
+			}
+		}
+		if (c == '\'' && state > INSQ && state < INDQ) {
+			state -= INSQ;
+			if (state < 0) {
+				break;
+			}
+		}
+		if (c == '\'' && state < INSQ) {
+			state += INSQ;
+			if (state >= (INSQ * 2)) {
+				break;
+			}
+		}
+	}
+
+	if (state != 0) {
+		printf("SYNTAX ERROR: ");
+		
+		if (state >= INSQ && state < INDQ) {
+			printf("Unclosed single quote on line %d!\n", linenr);
+			return 1;
+		}
+		if (counts[PARENS] > 0) {
+			printf("Unclosed parenthesis on line %d!\n", linenr);
+			return 1;
+		}
+		if (counts[PARENS] < 0) {
+			printf("Too many close parentheses on line %d!\n", linenr);
+			return 1;
+		}
+		if (counts[BRACKETS] > 0) {
+			printf("Unclosed brackets on line %d!\n", linenr);
+			return 1;
+		}
+		if (counts[BRACKETS] < 0) {
+			printf("Too many close brackets on line %d!\n", linenr);
+			return 1;
+		}
+		if (counts[BRACES] > 0) {
+			printf("Unclosed braces on line %d!\n", linenr);
+			return 1;
+		}
+		if (counts[BRACES] < 0) {
+			printf("Too many close braces on line %d!\n", linenr);
+			return 1;
+		}
+	}
+
+	printf("All clean.\n");
+	return 0;
+}
-- 
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