examples: don't promote unchecked function calls

* etc/bench.pl.in, examples/c/bistromathic/parse.y,
* examples/c/calc/calc.y, examples/c/pushcalc/calc.y: Check scanf's
return value.
* doc/bison.texi: Likewise, but only for the second example, to avoid
cluttering the very simple case.

TODO

@@ -7,6 +7,8 @@
 - How about not evaluating incomplete lines when the text is not finished
   (as shells do).
 
+- Caret diagnostics
+
 ** Doc
 *** api.header.include
 

doc/bison.texi

@@ -2656,6 +2656,7 @@ found, a pointer to that symbol is returned; otherwise zero is returned.
    always succeed, and that integer calculations
    never overflow.  Production-quality code should
    not make these assumptions.  */
+#include <assert.h>
 #include <stdlib.h> /* malloc, realloc. */
 #include <string.h> /* strlen. */
 @end group
@@ -2728,7 +2729,8 @@ yylex (void)
   if (c == '.' || isdigit (c))
     @{
       ungetc (c, stdin);
-      scanf ("%lf", &yylval.NUM);
+      int n = scanf ("%lf", &yylval.NUM);
+      assert (n == 1);
       return NUM;
     @}
 @end group

etc/bench.pl.in

@@ -498,7 +498,8 @@ yylex (void)
     case '5': case '6': case '7': case '8': case '9':
       {
         int nchars = 0;
-        sscanf (input - 1, "%d%n", &yylval.NUM, &nchars);
+        int n = sscanf (input - 1, "%d%n", &yylval.NUM, &nchars);
+        assert (n == 1);
         input += nchars - 1;
         return NUM;
       }

examples/c/bistromathic/parse.y

@@ -268,7 +268,8 @@ yylex (const char **line, YYSTYPE *yylval, YYLTYPE *yylloc)
     case '5': case '6': case '7': case '8': case '9':
       {
         int nchars = 0;
-        sscanf (*line - 1, "%lf%n", &yylval->TOK_NUM, &nchars);
+        int n = sscanf (*line - 1, "%lf%n", &yylval->TOK_NUM, &nchars);
+        assert (n == 1);
         *line += nchars - 1;
         yylloc->last_column += nchars - 1;
         return TOK_NUM;
@@ -284,7 +285,8 @@ yylex (const char **line, YYSTYPE *yylval, YYLTYPE *yylloc)
       {
         int nchars = 0;
         char buf[100];
-        sscanf (*line - 1, "%99[a-z]%n", buf, &nchars);
+        int n = sscanf (*line - 1, "%99[a-z]%n", buf, &nchars);
+        assert (n == 1);
         *line += nchars - 1;
         yylloc->last_column += nchars - 1;
         if (strcmp (buf, "exit") == 0)

examples/c/calc/calc.y

@@ -1,4 +1,5 @@
 %code top {
+  #include <assert.h>
   #include <ctype.h>  /* isdigit. */
   #include <stdio.h>  /* For printf, etc. */
   #include <string.h> /* strcmp. */
@@ -73,7 +74,8 @@ yylex (void)
   if (c == '.' || isdigit (c))
     {
       ungetc (c, stdin);
-      scanf ("%lf", &yylval.NUM);
+      int n = scanf ("%lf", &yylval.NUM);
+      assert (n == 1);
       return NUM;
     }
 

examples/c/pushcalc/calc.y

@@ -1,6 +1,6 @@
 %code top {
+  #include <assert.h>
   #include <ctype.h>  /* isdigit. */
-  #include <stdbool.h>
   #include <stdio.h>  /* For printf, etc. */
   #include <string.h> /* strcmp. */
 }
@@ -81,7 +81,8 @@ yylex (YYSTYPE *yylval)
   if (c == '.' || isdigit (c))
     {
       ungetc (c, stdin);
-      scanf ("%lf", &yylval->NUM);
+      int n = scanf ("%lf", &yylval->NUM);
+      assert (n == 1);
       return NUM;
     }