refactoring: Rename one variable and replace decimal values with their character signs in order to increase comprehensibility and readability.

src/stringManipulation.c

@@ -80,14 +80,14 @@ bool everyCharacterIsDigit(char *string)
 }
 
 bool isLetterOfAlphabet(char *string){
-	bool r = true;
+	bool everyCharIsInAlphabet = true;
 	for(int i=0;*(string+i)!='\0';++i){
-		if( !(*(string+i)>=65&&*(string+i)<=90) && !(*(string+i)>=97&&*(string+i)<=122)){
-			r = false;
+		if( !(*(string+i)>='A'&&*(string+i)<='Z') && !(*(string+i)>='a'&&*(string+i)<='z')){
+			everyCharIsInAlphabet = false;
 			break;
 		}
 	}
-	return r;	
+	return everyCharIsInAlphabet;	
 }
 
 unsigned int toUnsignedInteger(char *ID)