[ub] small fixes to examples (#7890)

Author: notadragon

source/ub.tex

@@ -790,23 +790,20 @@
 
 \pnum
 \begin{example}
+If \tcode{float} does not adhere to \IsoFloatUndated{}
+and cannot represent positive infinty,
+a sufficiently large \tcode{double} value will be
+outside the (finite) range of \tcode{float}.
 \begin{codeblock}
 void f() {
-  double d = FLT_MAX * 16;
+  double d = FLT_MAX;
   d *= 16;
   float f = static_cast<float>(d);  // undefined behavior.
 }
 \end{codeblock}
 \end{example}
 
 
-\pnum
-\begin{example}
-\begin{codeblock}
-
-\end{codeblock}
-\end{example}
-
 \pnum
 \ubxref{expr.static.cast.downcast.wrong.derived.type} \\
 Down-casting to the wrong derived type is undefined behavior.
@@ -1347,7 +1344,8 @@
 \begin{codeblock}
 extern int &ir1;
 int i2 = ir1;   // undefined behavior, \tcode{ir1} not yet initialized
-int ir1 = 17;
+int i3 = 17;
+int &ir1 = i3;
 \end{codeblock}
 \end{example}
 
@@ -1674,9 +1672,9 @@
 }
 void f()
 {
-  X& px = &g();
+  X* px = &g();
   px->~X();
-  int*p = px->i;    // undefined behavior
+  int j = px->i;    // undefined behavior
 }
 \end{codeblock}
 \end{example}