KNR C exercise 1-14 implementation with some really cool optimization and tricks.

KNR C/ex1_14.c

@@ -0,0 +1,80 @@
+#include <stdio.h>
+
+/*Initial implementation of KNR C Exercise 1-14*/
+
+int main(){
+
+	/*Reference array that stores literal characters to be searched later by a
+	 * for loop, obtaining their position in the array, and therefore knowing
+	 * what position to add them to in charCount without needing a special case
+	 * for every possible character. While it is possible to exploit the ascii
+	 * table to do this procedurally, this is faster by virtue of initializing
+	 * at compile time rather than run time*/
+	int refTable [27] = { ' ' , 'a' , 'b' , 'c' , 'd' , 'e' , 'f', 'g' , 'h' ,
+	'i' , 'j' , 'k' , 'l' , 'm' , 'n', 'o' , 'p' , 'q' , 'r' , 's' , 't' , 'u' ,
+	'v' , 'w' , 'x' , 'y' , 'z'};
+
+	/*Initialize an array of labels for the numerical table later. This looks
+	 * wierd since it's mostly refTable[] again, but again, we do this at
+	 * copile rather than procedurally in order to avoid adding an extra if
+	 * statement on the print loop to look for the specific case where i is 
+	 * 0 or 27 and print a different character that isn't in refTable*/
+	/*TODO find a way to do this so that # and ! are replaced by WSPC and PCTN
+	 * respectively*/
+	int printTable [28] = { '#' , 'a' , 'b' , 'c' , 'd' , 'e' , 'f', 'g' , 'h' ,
+	'i' , 'j' , 'k' , 'l' , 'm' , 'n', 'o' , 'p' , 'q' , 'r' , 's' , 't' , 'u' ,
+	'v' , 'w' , 'x' , 'y' , 'z' , '!'};
+
+	/*Initialize character count storage array. Whitespaces are stored at pos 0
+	 * while letters are stored at their numeric positions in the alphabet, and
+	 * punchtuation is stored at position 27.*/
+	int charCount[28] = { 0 };
+	int i = 0;
+
+
+	/*Begin input text enumeration loop...*/
+	for(int a = getchar(); a != EOF; a = getchar()){
+		/*Begin whitespace filter check*/
+		if(a == '\n' || a == ' ' || a == '\t'){
+			++ charCount[0];
+			continue; /*Escape and restart loop to avoid running redundant
+						tests.*/
+		}
+
+		/*Begin refTable search loop; check if a = current pos in the refTable
+		 * array, increment that position in charCount[], otherwise, increment
+		 * i and check again. In any case, break on condition met or value i 
+		 * out of expected range.*/
+		for(i = 1; i <= 27; ++i){
+			if(a == refTable[i]){
+				++charCount[i];
+				break;
+			} else if(i == 27){
+				++charCount[27]; /*Increments charCount[27] on unspecified char
+								   thus preventing hangs on unspecified input*/
+				break;
+			} 
+		}
+	}
+	/*Input text enumeration complete; set values in refTable for printing...*/
+
+
+	/*Begin output generation...*/
+	/*Vertical table of numerical values:*/
+	for(int i=0; i <= 27; ++i)
+		printf("%4c %4d\n", printTable[i], charCount[i]);
+	
+	/*Print a histogram of gathered data (recycled from ex1_13_improved.c.*/
+	i = 0;
+	printf("\nHistogram of letters encountered.\n");
+	for (int b = charCount[i]; i <= 27; ++i){
+		printf ("%1c ", printTable[i]);
+		for (; b > 0; --b){
+			printf("|");
+		}
+		printf("\n");
+		b = charCount[(i + 1)];
+	}
+	
+return 0;
+}