add a note on prefix matches with C strings

content/programming/blog/cstring-starts-with.tree

@@ -0,0 +1,17 @@
+%% title = "prefix matches with C strings"
+
+% id = "01JCGAM55352EF247HZ358BAJ8"
+- one thing I realised while reading some code at work that worked with C strings: it's surprising how easy it is to match a prefix on a C string.
+
+```c
+if (s != NULL
+    && s[0] == 'h'
+    && s[1] == 'u'
+    && s[2] == 'g')
+{
+    // ...
+}
+```
+
+% id = "01JCGAM5537WYE3GEN6WGX8WD0"
+- this works because of the NUL terminator---if it appears at any point in the string, the `s[i] == c` comparison will return `false`, thus breaking the `&&` chain---so indices always stay in-bounds!