refresh

sk2/calculator.c

@@ -5,20 +5,20 @@
 #include <string.h>
 #include <math.h>
 
-static const char *ptr;
+static const char *cur;
 
 
 
-static void skip_spaces(void) {
+static void skip_ws(void) {
-    while (*ptr && isspace(*ptr)) {
+    while (*cur && isspace(*cur)) {
-        ptr++;
+        cur++;
     }
 }
 
-static int match(const char *s) {
+static int starts_with(const char *name) {
-    int len = strlen(s);
+    int len = strlen(name);
-    if (strncmp(ptr, s, len) == 0) {
+    if (strncmp(cur, name, len) == 0) {
-        ptr += len;
+        cur += len;
         return 1;
     }
     return 0;
@@ -26,104 +26,101 @@ static int match(const char *s) {
 
 
 
-static double parse_expression(void);
+static double read_expr(void);
 
-static double parse_number(void) {
+static double read_number(void) {
-    skip_spaces();
+    skip_ws();
     char *end;
-    double val = strtod(ptr, &end);
+    double res = strtod(cur, &end);
-    ptr = end;
+    cur = end;
-    return val;
+    return res;
 }
 
-static double parse_factor(void) {
+static double read_factor(void) {
-    skip_spaces();
+    skip_ws();
 
-    
+    if (*cur == '(') {
-    if (*ptr == '(') {
+        cur++;
-        ptr++;
+        double res = read_expr();
-        double val = parse_expression();
+        skip_ws();
-        skip_spaces();
+        if (*cur == ')') {
-        if (*ptr == ')') {
+            cur++;
-            ptr++;
         }
-        return val;
+        return res;
     }
 
-   
+    if (starts_with("sin")) {
-    if (match("sin")) {
+        skip_ws();
-        skip_spaces();
+        return sin(read_factor());
-        return sin(parse_factor());
     }
-    if (match("cos")) {
+    if (starts_with("cos")) {
-        skip_spaces();
+        skip_ws();
-        return cos(parse_factor());
+        return cos(read_factor());
     }
-    if (match("sqrt")) {
+    if (starts_with("sqrt")) {
-        skip_spaces();
+        skip_ws();
-        return sqrt(parse_factor());
+        return sqrt(read_factor());
     }
-    if (match("log")) {
+    if (starts_with("log")) {
-        skip_spaces();
+        skip_ws();
-        return log(parse_factor());
+        return log(read_factor());
     }
-    if (match("pow")) {
+    if (starts_with("pow")) {
-        skip_spaces();
+        skip_ws();
-        if (*ptr == '(') ptr++;
+        if (*cur == '(') cur++;
-        double a = parse_expression();
+        double left = read_expr();
-        skip_spaces();
+        skip_ws();
-        if (*ptr == ',') ptr++;
+        if (*cur == ',') cur++;
-        double b = parse_expression();
+        double right = read_expr();
-        skip_spaces();
+        skip_ws();
-        if (*ptr == ')') ptr++;
+        if (*cur == ')') cur++;
-        return pow(a, b);
+        return pow(left, right);
     }
 
-    
+    return read_number();
-    return parse_number();
 }
 
-static double parse_term(void) {
+static double read_term(void) {
-    double val = parse_factor();
+    double res = read_factor();
 
     while (1) {
-        skip_spaces();
+        skip_ws();
-        if (*ptr == '*') {
+        if (*cur == '*') {
-            ptr++;
+            cur++;
-            val *= parse_factor();
+            res *= read_factor();
-        } else if (*ptr == '/') {
+        } else if (*cur == '/') {
-            ptr++;
+            cur++;
-            val /= parse_factor();
+            res /= read_factor();
         } else {
             break;
         }
     }
 
-    return val;
+    return res;
 }
 
-static double parse_expression(void) {
+static double read_expr(void) {
-    double val = parse_term();
+    double res = read_term();
 
     while (1) {
-        skip_spaces();
+        skip_ws();
-        if (*ptr == '+') {
+        if (*cur == '+') {
-            ptr++;
+            cur++;
-            val += parse_term();
+            res += read_term();
-        } else if (*ptr == '-') {
+        } else if (*cur == '-') {
-            ptr++;
+            cur++;
-            val -= parse_term();
+            res -= read_term();
         } else {
             break;
         }
     }
 
-    return val;
+    return res;
 }
 
 
 
 double evaluate_expression(const char *expr) {
-    ptr = expr;
+    cur = expr;
-    return parse_expression();
+    return read_expr();
 }