implemented stringToDouble feature

cstring.h

@@ -363,6 +363,40 @@ int64_t stringFindFirstCharArr(TString s, const char *pattern) {
     return -1; 
 }
 
+double stringToDouble(TString s) {
+    double result = 0.0;
+    int sign = 1;
+    int decimalIndex = -1;
+    if (s.size > 0 && s.data[0] == '-') {
+        sign = -1;
+        stringRemove(&s, 0, 1);
+    }
+    for (size_t i = 0; i < s.size; ++i) {
+        if (s.data[i] == '.') {
+            decimalIndex = i;
+            break;
+        }
+    }
+    for (size_t i = 0; i < s.size; ++i) {
+        if (s.data[i] == '.') {
+            break;
+        }
+        if (stringCharIsDigit(s.data[i])) {
+            result = result * 10.0 + (s.data[i] - '0');
+        }
+    }
+    double divisor = 10.0;
+    if (decimalIndex != -1) {
+        for (size_t i = decimalIndex + 1; i < s.size; ++i) {
+            if (stringCharIsDigit(s.data[i])) {
+                result += (s.data[i] - '0') / divisor;
+                divisor *= 10.0;
+            }
+        }
+    }
+    return sign * result;
+}
+
 TString stringInit(size_t capacity) {
     TString s = {0};
     s.data = (char *) malloc(sizeof(char) * capacity);

tests/main.c

@@ -372,6 +372,22 @@ void test_stringContains() {
     printGreen("test_stringContains\n");
 }
 
+void test_stringToDouble() {
+    TString s1 = stringInitWithCharArr("3.14159");
+    TString s2 = stringInitWithCharArr("123");
+    TString s3 = stringInitWithCharArr("-100");
+
+    assertEq(stringToDouble(s1), 3.14159);
+    assertEq(stringToDouble(s2), 123);
+    assertEq(stringToDouble(s3), -100);
+
+    stringDestroy(&s1);
+    stringDestroy(&s2);
+    stringDestroy(&s3);
+
+    printGreen("test_stringToDouble\n");
+}
+
 bool acceptAll(char c) {
     return true;
 }