add problem 28 and test function

Author: supercoderhawk

C/1-50/28-Implement-strStr().c

@@ -0,0 +1,44 @@
+/*
+ * Implement strStr().
+
+ * Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
+ * Created by supercoderx on 2017/8/11.
+ */
+#include 
+
+int strStr(char *haystack, char *needle) {
+    int len = 0, subLen = 0, diff = 0, isContain = 1;
+    char *str = haystack;
+    while (*str != '\0') {
+        len++;
+        str++;
+    }
+    str = needle;
+    while (*str != '\0') {
+        subLen++;
+        str++;
+    }
+
+    if (subLen > len)
+        return -1;
+
+    diff = len - subLen;
+    for (int i = 0; i < diff + 1; i++) {
+        for (int j = i; j < i + subLen; j++) {
+            if (haystack[j] != needle[j - i]) {
+                isContain = 0;
+                break;
+            }
+        }
+        if (isContain == 1)
+            return i;
+        isContain = 1;
+    }
+    return -1;
+}
+
+void testStrStr() {
+    char *s1 = "abcdefg";
+    char *s2 = "bcd";
+    printf("%d", strStr(s1, s2));
+}