diff --git a/parse.y b/parse.y
index 89a05b1..0bdd8a3 100644
--- a/parse.y
+++ b/parse.y
@@ -29,6 +29,8 @@
 
 #include "units.h"
 
+int yylex();
+void yyerror(char *);
 
 static int err;  /* value used by parser to store return values */
 
@@ -114,7 +116,7 @@ funcunit(struct unittype *theunit, struct function *fun)
     if (err)
       return err;
   } else if (fun->type==ANGLEOUT || fun->type == DIMENSIONLESS) {
-    if (err=unit2num(theunit))
+    if ((err=unit2num(theunit)))
       return err;
     
   } else 
@@ -278,7 +280,7 @@ struct {
                  "per" , DIVIDE, 
                  0, 0 };
 
-yylex(YYSTYPE *lvalp, struct commtype *comm)
+int yylex(YYSTYPE *lvalp, struct commtype *comm)
 {
   int length, count;
   struct unittype *output;
@@ -414,7 +416,7 @@ yylex(YYSTYPE *lvalp, struct commtype *comm)
 }
 
 
-yyerror(char *s){}
+void yyerror(char *s){}
 
 void
 freelist(int startunit)
diff --git a/units.c b/units.c
index f5416b0..2cd6765 100644
--- a/units.c
+++ b/units.c
@@ -29,6 +29,7 @@
 
 #ifdef READLINE
 #  include <readline/readline.h>
+#  include <readline/history.h>
 #  define RVERSTR "with readline"
 #else
 #  define RVERSTR "without readline"
@@ -489,7 +490,7 @@ readunits(char *file, FILE *errfile,
       }	
       if (wronglocale)
 	continue;
-      if (lineptr = strchr(line,COMMENTCHAR))
+      if ((lineptr = strchr(line,COMMENTCHAR)))
          *lineptr = 0;
       unitname = strtok(line, WHITE);
       if (!unitname || !*unitname) 
@@ -519,9 +520,9 @@ readunits(char *file, FILE *errfile,
   	     goterr=1;
 	     continue;
 	 }
-	 if (pfxptr = plookup(unitname)) {  /* already there: redefinition */
+	 if ((pfxptr = plookup(unitname))) {  /* already there: redefinition */
  	    goterr=1;
-            if (errfile)
+            if (errfile) {
 	      if (!strcmp(pfxptr->name, unitname))
 		fprintf(errfile,
    	        "%s: redefinition of prefix '%s-' on line %d of '%s' ignored.\n",
@@ -529,6 +530,7 @@ readunits(char *file, FILE *errfile,
 	      else
 	         fprintf(errfile, "%s: prefix '%s-' on line %d of '%s' is hidden by earlier definition of '%s-'.\n",
 		       progname, unitname, linenum, file, pfxptr->name);
+            }
 	    continue;
 	 } 
 
@@ -948,7 +950,7 @@ lookupunit(char *unit,int prefixok)
    struct prefixlist *pfxptr;
    struct unitlist *uptr;
 
-   if (uptr = ulookup(unit))
+   if ((uptr = ulookup(unit)))
       return uptr->value;
 
    if (strlen(unit)>2 && unit[strlen(unit) - 1] == 's') {
@@ -1278,7 +1280,7 @@ completereduce(struct unittype *unit)
 {
    int err;
 
-   if (err=reduceunit(unit))
+   if ((err=reduceunit(unit)))
      return err;
    sortunit(unit);
    cancelunit(unit);
@@ -1340,7 +1342,7 @@ unit2num(struct unittype *input)
   int err;
 
   initializeunit(&one);
-  if (err=completereduce(input))
+  if ((err=completereduce(input)))
     return err;
   if (compareunits(input,&one,ignore_nothing))
     return E_NOTANUMBER;
@@ -1404,13 +1406,13 @@ rootunit(struct unittype *inunit,int n)
    int err; 
 
    initializeunit(&outunit);
-   if (err=completereduce(inunit))
+   if ((err=completereduce(inunit)))
      return err;
-   if ((n & 1==0) && (inunit->factor<0)) return E_NOTROOT;
+   if (((n & 1)==0) && (inunit->factor<0)) return E_NOTROOT;
    outunit.factor = pow(inunit->factor,1.0/(double)n);
-   if (err = subunitroot(n, inunit->numerator, outunit.numerator))
+   if ((err = subunitroot(n, inunit->numerator, outunit.numerator)))
      return err;
-   if (err = subunitroot(n, inunit->denominator, outunit.denominator))
+   if ((err = subunitroot(n, inunit->denominator, outunit.denominator)))
      return err;
    freeunit(inunit);
    initializeunit(inunit);
@@ -1482,9 +1484,9 @@ addunit(struct unittype *unita, struct unittype *unitb)
 {
   int err;
 
-  if (err=completereduce(unita))
+  if ((err=completereduce(unita)))
     return err;
-  if (err=completereduce(unitb))
+  if ((err=completereduce(unitb)))
     return err;
   if (compareunits(unita,unitb,ignore_nothing))
     return E_BADSUM;
@@ -1723,7 +1725,7 @@ showanswer(char *havestr,struct unittype *have,
 {
    struct unittype invhave;
    int doingrec;  /* reciprocal conversion? */
-   char *sep, *right, *left;
+   char *sep = NULL, *right = NULL, *left = NULL;
 
    doingrec=0;
    havestr = removepadding(havestr);
@@ -1970,7 +1972,8 @@ addtolist(struct unittype *have, char *searchstring, char *rname, char *name, ch
 	       int *count, int searchtype)
 {
   struct unittype want;
-  int len,keepit;
+  int len = 0;
+  int keepit = 0;
 
   if (!name) 
     return;
@@ -2243,7 +2246,7 @@ completeunits(char *text, int state)
       curunit = utab[uhash];
     }
     if (!curunit && !curprefix){
-      if (curprefix = plookup(text)){
+      if ((curprefix = plookup(text))){
         if (strlen(curprefix->name)>1 && strlen(curprefix->name)<strlen(text)){
           uhash = 0;
           curunit = utab[uhash];
@@ -2481,7 +2484,7 @@ processunit(struct unittype *theunit, char *unitstr, char *prompt, int pointer)
   char *errmsg;
   int errloc,err;
 
-  if (err=parseunit(theunit, unitstr, &errmsg, &errloc)){
+  if ((err=parseunit(theunit, unitstr, &errmsg, &errloc))){
     if (pointer){
       if (err!=E_UNKNOWNUNIT || !irreducible){
 	if (!quiet) {
@@ -2501,7 +2504,7 @@ processunit(struct unittype *theunit, char *unitstr, char *prompt, int pointer)
 
     return 1;
   }
-  if (err=completereduce(theunit)){
+  if ((err=completereduce(theunit))){
     printf("%s",errormsg[err]);
     if (err==E_UNKNOWNUNIT)
       printf(" '%s'", irreducible);
@@ -2584,11 +2587,11 @@ Typing 'search text' will show units whose names contain 'text'.\n\n",
              UNITMATCH);
       return 1;
     }
-    if (function = isfunction(str)){
+    if ((function = isfunction(str))){
       file = function->file;
       unitline = function->linenumber;
     }
-    else if (unit = ulookup(str)){
+    else if ((unit = ulookup(str))){
       unitline = unit->linenumber;
       file = unit->file;
     }
@@ -2678,7 +2681,7 @@ main(int argc, char **argv)
    }
 
    if (!interactive) {
-      if (funcval = isfunction(havestr)){
+      if ((funcval = isfunction(havestr))){
 	showfuncdefinition(funcval);
   	exit(0);
       }
@@ -2688,7 +2691,7 @@ main(int argc, char **argv)
          showdefinition(havestr,&have);
          exit(0);
       }
-      if (funcval = isfunction(wantstr)){
+      if ((funcval = isfunction(wantstr))){
          if (showfunc(havestr, &have, funcval))
 	   exit(1);
 	 else
@@ -2710,7 +2713,7 @@ main(int argc, char **argv)
 	 } while (isblankstr(havestr) || ishelpquery(havestr,0) ||
 		  (isfunction(havestr)==0 
 		  && processunit(&have, havestr, queryhave, POINT)));
-         if (funcval = isfunction(havestr)){
+         if ((funcval = isfunction(havestr))){
 	   showfuncdefinition(funcval);
 	   continue;
 	 }
@@ -2728,7 +2731,7 @@ main(int argc, char **argv)
 		  && processunit(&want, wantstr, querywant, POINT));
          if (isblankstr(wantstr))
            showdefinition(havestr,&have);
-         else if (funcval = isfunction(wantstr))
+         else if ((funcval = isfunction(wantstr)))
            showfunc(havestr, &have, funcval);
 	 else {
            showanswer(havestr,&have,wantstr, &want);