From 5018e06c580dd21c958ec1672c26a3448faf0c55 Mon Sep 17 00:00:00 2001
From: zlg <zlg@zlg.space>
Date: Wed, 13 Feb 2013 20:48:44 -0600
Subject: Add license file, reorganize project

---
 ch1/1-24_syntax-checker.c | 163 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 163 insertions(+)
 create mode 100644 ch1/1-24_syntax-checker.c

(limited to 'ch1/1-24_syntax-checker.c')

diff --git a/ch1/1-24_syntax-checker.c b/ch1/1-24_syntax-checker.c
new file mode 100644
index 0000000..019b9bc
--- /dev/null
+++ b/ch1/1-24_syntax-checker.c
@@ -0,0 +1,163 @@
+#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.
+ *
+ * Post-solution note: switch() would've made this MUCH shorter...
+ */
+
+char c;
+
+/* Set the state/count variables */
+int linenr, parens, brackets, braces, singqs, dubqs, escapes, mcomms, scomms = 0;
+
+int main() {
+	linenr = 1;
+	// Begin streaming!
+	while ((c = getchar()) != EOF) {
+		if (scomms == 1) {
+			if (c == '\n') {
+				scomms--;
+			} else {
+				continue;
+			}
+		} else if (mcomms == 1) {
+			if (c == '*') {
+				if (getchar() == '/') {
+					mcomms--;
+				}
+			}
+		} else {
+			// Check for escape sequences
+			if (c == '\\') {
+				escapes++;
+				c = getchar();
+				// This does not detect all sequences; just the ones covered in Chapter 1.
+				if (c != '\\' && c != 't' && c != '\'' && c != '"' && c != 'n' && c != 'b' && c != '0') {
+					break;
+				} else {
+					escapes--;
+				}
+			}
+			// Newline behavior
+			if (c == '\n') {
+				if (singqs > 0 || dubqs > 0) {
+					break;
+				}
+				linenr++;
+			}
+			// Parentheses
+			if (c == '(') {
+				parens++;
+			}
+			if (c == ')') {
+				parens -= 1;
+				if (parens < 0) {
+					break;
+				}
+			}
+			// Brackets
+			if (c == '[') {
+				brackets++;
+			}
+			if (c == ']') {
+				brackets--;
+				if (brackets < 0) {
+					break;
+				}
+			}
+			// Braces
+			if (c == '{') {
+				braces++;
+			}
+			if (c == '}') {
+				braces--;
+				if (braces < 0) {
+					break;
+				}
+			}
+			// Double quotes
+			if (c == '"') {
+				if (dubqs == 0) {
+					dubqs++;
+				} else {
+					dubqs--;
+				}
+			}
+			// Single quotes, which are only checked outside of doubles.
+			if (c == '\'' && dubqs == 0) {
+				if (singqs == 0) {
+					singqs++;
+				} else {
+					singqs--;
+				}
+			}
+			// Comment detection
+			if (c == '/') {
+				if (getchar() == '*') {
+					mcomms++;
+				}
+				if (getchar() == '/') {
+					scomms++;
+				}
+			}
+		}
+	}
+
+	if (escapes > 0) {
+		printf("Invalid escape sequence on line %d!\n", linenr);
+		return 1;
+	}
+	if (singqs > 0) {
+		printf("Unclosed single quote on line %d!\n", linenr);
+		return 1;
+	}
+	if (dubqs > 0) {
+		printf("Unclosed double quote on line %d!\n", linenr);
+		return 1;
+	}
+	if (brackets > 0) {
+		printf("Unclosed brackets on line %d!\n", linenr);
+		return 1;
+	}
+	if (brackets < 0) {
+		printf("Too many close brackets on line %d!\n", linenr);
+		return 1;
+	}
+	if (parens > 0) {
+		printf("Unclosed parenthesis on line %d!\n", linenr);
+		return 1;
+	}
+	if (parens < 0) {
+		printf("Too many close parentheses on line %d!\n", linenr);
+		return 1;
+	}
+	if (braces > 0) {
+		printf("Unclosed braces on line %d!\n", linenr);
+		return 1;
+	}
+	if (braces < 0) {
+		printf("Too many close braces on line %d!\n", linenr);
+		return 1;
+	}
+	if (mcomms == 1) {
+		printf("Unclosed comment at end of file!\n");
+		return 1;
+	}
+
+	printf("All clean.\n");
+	return 0;
+}
-- 
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