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#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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