alternating_characters file added

Author: kiruthikvishaal

Strings/alternating_characters.c

@@ -0,0 +1,10 @@
+int alternatingCharacters(String s) {
+    int a=strlen(s);
+    int k=0,i;
+    for(i=0;i<a;i++)
+    {
+        if(s[i]==s[i+1])
+            k++;
+    }
+    return k;
+}