diff --git a/src/frontend/aspice.c b/src/frontend/aspice.c
index c94c7c801..276a9a673 100644
--- a/src/frontend/aspice.c
+++ b/src/frontend/aspice.c
@@ -123,7 +123,7 @@ com_aspice(wordlist *wl)
         }
         (void) dup2(fileno(stdout), fileno(stderr));
 
-        (void) execl(spicepath, spicepath, "-r", raw, (void*)0);
+        (void) execl(spicepath, spicepath, "-r", raw, NULL);
 
         /* Screwed up. */
         perror(spicepath);
@@ -328,7 +328,7 @@ com_rspice(wordlist *wl)
         dup2(from_serv[1], 1);  /* stdout */
         dup2(err_serv[1], 2);   /* stderr */
 
-        execlp(remote_shell, remote_shell, rhost, program, "-s", (void*)0);
+        execlp(remote_shell, remote_shell, rhost, program, "-s", NULL);
         /* system(com_buf); */
         perror(remote_shell);
         exit(-1);
diff --git a/src/frontend/breakp.c b/src/frontend/breakp.c
index d9c6b49af..5582c761f 100644
--- a/src/frontend/breakp.c
+++ b/src/frontend/breakp.c
@@ -161,7 +161,7 @@ bad:
 void
 com_trce(wordlist *wl)
 {
-    settrace(wl, VF_PRINT, 0);
+    settrace(wl, VF_PRINT, NULL);
 }
 
 
diff --git a/src/frontend/commands.c b/src/frontend/commands.c
index bec672c31..e106188de 100644
--- a/src/frontend/commands.c
+++ b/src/frontend/commands.c
@@ -580,7 +580,7 @@ struct comm spcp_coms[] = {
       { 0, 0, 0, 0 }, E_DEFHMASK, 0, 0,
       NULL,
       ": Print circuit inventory" },
-    { 0, NULL, FALSE, FALSE,
+    { NULL, NULL, FALSE, FALSE,
       { 0, 0, 0, 0 }, E_DEFHMASK, 0, LOTS,
       NULL,
       NULL }
@@ -971,7 +971,7 @@ struct comm nutcp_coms[] = {
       { 0, 0, 0, 0 }, E_DEFHMASK, 0, 0,
       NULL,
       ": Print circuit inventory" } ,
-    { 0, NULL, FALSE, FALSE,
+    { NULL, NULL, FALSE, FALSE,
       { 0, 0, 0, 0 }, E_DEFHMASK, 0, LOTS,
       NULL,
       NULL }
diff --git a/src/frontend/control.c b/src/frontend/control.c
index 10cdcca2e..b87a21978 100644
--- a/src/frontend/control.c
+++ b/src/frontend/control.c
@@ -551,7 +551,7 @@ get_alt_prompt(void)
     struct control *c;
 
     /* if nothing on the command stack return NULL */
-    if (cend[stackp] == 0)
+    if (cend[stackp] == NULL)
         return NULL;
 
     /* measure stack depth */
diff --git a/src/frontend/device.c b/src/frontend/device.c
index e7cb99282..e6f6cd3be 100644
--- a/src/frontend/device.c
+++ b/src/frontend/device.c
@@ -734,7 +734,7 @@ listparam(wordlist *p, dgen *dg)
                     fprintf(cp_out, "%*.*s", LEFT_WIDTH, LEFT_WIDTH, p->wl_word);
                 else
                     fprintf(cp_out, "%*s", LEFT_WIDTH, " ");
-                k = dgen_for_n(dg, count, bogus1, 0, j);
+                k = dgen_for_n(dg, count, bogus1, NULL, j);
                 fprintf(cp_out, "\n");
                 j += 1;
             } while (k > 0);
@@ -746,7 +746,7 @@ listparam(wordlist *p, dgen *dg)
                 fprintf(cp_out, "%*.*s", LEFT_WIDTH, LEFT_WIDTH, p->wl_word);
             else
                 fprintf(cp_out, "%*s", LEFT_WIDTH, " ");
-            k = dgen_for_n(dg, count, bogus2, 0, j);
+            k = dgen_for_n(dg, count, bogus2, NULL, j);
             fprintf(cp_out, "\n");
             j += 1;
         } while (k > 0);
diff --git a/src/frontend/help/help.c b/src/frontend/help/help.c
index d1cfe8693..bee81e218 100644
--- a/src/frontend/help/help.c
+++ b/src/frontend/help/help.c
@@ -71,7 +71,7 @@ findglobalsubject(char *subject)
     char **dict;
     long fpos;
 
-    place = 0;
+    place = NULL;
     for (dict = hlp_filelist; *dict && **dict; dict++) {
         fpos = findsubject(*dict, subject);
         if (fpos != -1) {
diff --git a/src/frontend/help/readhelp.c b/src/frontend/help/readhelp.c
index a14cfc896..15ec41e6c 100644
--- a/src/frontend/help/readhelp.c
+++ b/src/frontend/help/readhelp.c
@@ -69,7 +69,7 @@ hlp_read(fplace *place)
     bool mof = FALSE;
 
     if (!place)
-        return 0;
+        return NULL;
 
     top->place = copy_fplace(place);
 
diff --git a/src/frontend/plotting/graf.c b/src/frontend/plotting/graf.c
index 304b56c00..d26aa5e16 100644
--- a/src/frontend/plotting/graf.c
+++ b/src/frontend/plotting/graf.c
@@ -612,7 +612,7 @@ iplot(struct plot *pl, int id)
     int yt;
     char *yl = NULL;
     double xlims[2], ylims[2];
-    static REQUEST reqst = { checkup_option, 0 };
+    static REQUEST reqst = { checkup_option, NULL };
     int inited = 0;
     char commandline[513];
 
@@ -680,7 +680,7 @@ iplot(struct plot *pl, int id)
 
     } else {
         /* plot the last points and resize if needed */
-        Input(&reqst, 0);
+        Input(&reqst, NULL);
         /* First see if we have to make the screen bigger */
         dy = (isreal(xs) ? xs->v_realdata[len - 1] :
               realpart(xs->v_compdata[len - 1]));
diff --git a/src/frontend/quote.c b/src/frontend/quote.c
index 9964434b5..cb62a19a6 100644
--- a/src/frontend/quote.c
+++ b/src/frontend/quote.c
@@ -91,6 +91,6 @@ cp_unquote(char *string)
 
         return (s);
     } else {
-        return 0;
+        return NULL;
     }
 }
diff --git a/src/frontend/rawfile.c b/src/frontend/rawfile.c
index de6527212..82e4322fa 100644
--- a/src/frontend/rawfile.c
+++ b/src/frontend/rawfile.c
@@ -293,7 +293,7 @@ raw_write(char *name, struct plot *pl, bool app, bool binary)
 struct plot *
 raw_read(char *name) {
     char *title = "default title";
-    char *date = 0;
+    char *date = NULL;
     struct plot *plots = NULL, *curpl = NULL;
     char buf[BSIZE_SP], *s, *t, *r;
     int flags = 0, nvars = 0, npoints = 0, i, j;
diff --git a/src/frontend/where.c b/src/frontend/where.c
index ef13fab8c..066f45a35 100644
--- a/src/frontend/where.c
+++ b/src/frontend/where.c
@@ -30,7 +30,7 @@ com_where(wordlist *wl)
         return;
     }
 
-    msg = ft_sim->nonconvErr (ft_curckt->ci_ckt, 0);
+    msg = ft_sim->nonconvErr (ft_curckt->ci_ckt, NULL);
 
     printf("%s", msg);
 
diff --git a/src/main.c b/src/main.c
index e12d01e83..bebfe10a5 100644
--- a/src/main.c
+++ b/src/main.c
@@ -448,7 +448,7 @@ EVTfindvec(char *node) {
 
 #endif /* SIMULATOR */
 
-char *hlp_filelist[] = { "ngspice", 0 };
+char *hlp_filelist[] = { "ngspice", NULL };
 
 
 /* allocate space for global constants in 'CONST.h' */
@@ -884,21 +884,21 @@ main(int argc, char **argv)
         enum { soa_log = 1001, };
 
         static struct option long_options[] = {
-            {"help",         no_argument,       0, 'h'},
-            {"version",      no_argument,       0, 'v'},
-            {"batch",        no_argument,       0, 'b'},
-            {"autorun",      no_argument,       0, 'a'},
-            {"circuitfile",  required_argument, 0, 'c'},
-            {"interactive",  no_argument,       0, 'i'},
-            {"no-spiceinit", no_argument,       0, 'n'},
-            {"output",       required_argument, 0, 'o'},
-            {"pipe",         no_argument,       0, 'p'},
-            {"completion",   no_argument,       0, 'q'},
-            {"rawfile",      required_argument, 0, 'r'},
-            {"server",       no_argument,       0, 's'},
-            {"terminal",     required_argument, 0, 't'},
-            {"soa-log",      required_argument, 0, soa_log},
-            {0, 0, 0, 0}
+            {"help",         no_argument,       NULL, 'h'},
+            {"version",      no_argument,       NULL, 'v'},
+            {"batch",        no_argument,       NULL, 'b'},
+            {"autorun",      no_argument,       NULL, 'a'},
+            {"circuitfile",  required_argument, NULL, 'c'},
+            {"interactive",  no_argument,       NULL, 'i'},
+            {"no-spiceinit", no_argument,       NULL, 'n'},
+            {"output",       required_argument, NULL, 'o'},
+            {"pipe",         no_argument,       NULL, 'p'},
+            {"completion",   no_argument,       NULL, 'q'},
+            {"rawfile",      required_argument, NULL, 'r'},
+            {"server",       no_argument,       NULL, 's'},
+            {"terminal",     required_argument, NULL, 't'},
+            {"soa-log",      required_argument, NULL, soa_log},
+            {NULL,           0,                 NULL, 0}
         };
 
         int option_index = 0;
diff --git a/src/maths/fft/fftext.c b/src/maths/fft/fftext.c
index c927965a5..f2528bcf7 100644
--- a/src/maths/fft/fftext.c
+++ b/src/maths/fft/fftext.c
@@ -42,18 +42,18 @@ int fftInit(int M)
     /*** I did NOT test cases with M>27 ***/
     if ((M >= 0) && ((size_t) M < 8*sizeof(int))) {
         theError = 0;
-        if (UtblArray[M] == 0) {	// have we not inited this size fft yet?
+        if (UtblArray[M] == NULL) {	// have we not inited this size fft yet?
             // init cos table
             UtblArray[M] = TMALLOC(double, POW2(M)/4+1);
-            if (UtblArray[M] == 0)
+            if (UtblArray[M] == NULL)
                 theError = 2;
             else {
                 fftCosInit(M, UtblArray[M]);
             }
             if (M > 1) {
-                if (BRLowArray[M/2] == 0) {	// init bit reversed table for cmplx fft
+                if (BRLowArray[M/2] == NULL) {	// init bit reversed table for cmplx fft
                     BRLowArray[M/2] = TMALLOC(short, POW2(M/2-1));
-                    if (BRLowArray[M/2] == 0)
+                    if (BRLowArray[M/2] == NULL)
                         theError = 2;
                     else {
                         fftBRInit(M, BRLowArray[M/2]);
@@ -61,9 +61,9 @@ int fftInit(int M)
                 }
             }
             if (M > 2) {
-                if (BRLowArray[(M-1)/2] == 0) {	// init bit reversed table for real fft
+                if (BRLowArray[(M-1)/2] == NULL) {	// init bit reversed table for real fft
                     BRLowArray[(M-1)/2] = TMALLOC(short, POW2((M-1)/2-1));
-                    if (BRLowArray[(M-1)/2] == 0)
+                    if (BRLowArray[(M-1)/2] == NULL)
                         theError = 2;
                     else {
                         fftBRInit(M-1, BRLowArray[(M-1)/2]);
@@ -80,15 +80,15 @@ void fftFree(void)
 // release storage for all private cosine and bit reversed tables
     int i1;
     for (i1=8*sizeof(int)/2-1; i1>=0; i1--) {
-        if (BRLowArray[i1] != 0) {
+        if (BRLowArray[i1] != NULL) {
             free(BRLowArray[i1]);
-            BRLowArray[i1] = 0;
+            BRLowArray[i1] = NULL;
         }
     }
     for (i1=8*sizeof(int)-1; i1>=0; i1--) {
-        if (UtblArray[i1] != 0) {
+        if (UtblArray[i1] != NULL) {
             free(UtblArray[i1]);
-            UtblArray[i1] = 0;
+            UtblArray[i1] = NULL;
         }
     }
 }
diff --git a/src/spicelib/analysis/cktpzstr.c b/src/spicelib/analysis/cktpzstr.c
index c28a6b79f..8e50d8e22 100644
--- a/src/spicelib/analysis/cktpzstr.c
+++ b/src/spicelib/analysis/cktpzstr.c
@@ -125,8 +125,8 @@ CKTpzFindZeros(CKTcircuit *ckt, PZtrial **rootinfo, int *rootcount)
     NIpzK_mag = 0;
     High_Guess = -1.0;
     Low_Guess = 1.0;
-    ZeroTrial = 0;
-    Trials = 0;
+    ZeroTrial = NULL;
+    Trials = NULL;
     NZeros = 0;
     NFlat = 0;
     Max_Zeros = SMPmatSize(ckt->CKTmatrix);
diff --git a/src/spicelib/analysis/cktsens.c b/src/spicelib/analysis/cktsens.c
index c181ae311..0c69fffa5 100644
--- a/src/spicelib/analysis/cktsens.c
+++ b/src/spicelib/analysis/cktsens.c
@@ -87,9 +87,9 @@ int sens_sens(CKTcircuit *ckt, int restart)
 	IFuid		*output_names, freq_name;
 	int		bypass;
 	int		type;
-	double		*saved_rhs = 0,
-			*saved_irhs = 0;
-	SMPmatrix	*saved_matrix = 0;
+	double		*saved_rhs = NULL,
+			*saved_irhs = NULL;
+	SMPmatrix	*saved_matrix = NULL;
 
 #ifndef notdef
 #ifdef notdef
diff --git a/src/spicelib/analysis/cktsetup.c b/src/spicelib/analysis/cktsetup.c
index 446749094..5aba27882 100644
--- a/src/spicelib/analysis/cktsetup.c
+++ b/src/spicelib/analysis/cktsetup.c
@@ -147,7 +147,7 @@ CKTunsetup(CKTcircuit *ckt)
     /* added by HT 050802*/
     for(node=ckt->CKTnodes;node;node=node->next){
         if(node->icGiven || node->nsGiven) {
-            node->ptr=0;
+            node->ptr=NULL;
         }
     }
 
diff --git a/src/spicelib/devices/hfet1/hfetload.c b/src/spicelib/devices/hfet1/hfetload.c
index 5222fa995..4e93bb3ad 100644
--- a/src/spicelib/devices/hfet1/hfetload.c
+++ b/src/spicelib/devices/hfet1/hfetload.c
@@ -721,8 +721,8 @@ cgd_calc:
     dtdvds      = deltdvdse*dvdsevds+deltdvkneet*CK1*temp;
     *gmd        = -delcgdvgs*dvdsevds+delcgdtd*dtdvds;
   } else {
-    gmg = 0;
-    gmd = 0;
+    gmg = NULL;
+    gmd = NULL;
   }  
 
   if(model->HFETAgatemod != 0) {  
diff --git a/src/xspice/cmpp/writ_ifs.c b/src/xspice/cmpp/writ_ifs.c
index 651f77232..bf9ca50ac 100644
--- a/src/xspice/cmpp/writ_ifs.c
+++ b/src/xspice/cmpp/writ_ifs.c
@@ -1251,7 +1251,7 @@ static char  *boolean_to_str(Boolean_t value)
         default:
             print_error("INTERNAL ERROR - boolean_to_str() - Impossible boolean value.");
 	    {
-	       char *p = 0; *p = 0;
+	       char *p = NULL; *p = 0;
 	    }
     }
 
diff --git a/src/xspice/ipc/ipctiein.c b/src/xspice/ipc/ipctiein.c
index cbf6553be..37550a27c 100644
--- a/src/xspice/ipc/ipctiein.c
+++ b/src/xspice/ipc/ipctiein.c
@@ -479,7 +479,7 @@ void ipc_free_devices(
     for(i = 0; i < num_items; i++)
 	{
         FREE(names[i]);
-		names[i] = 0;
+		names[i] = NULL;
 	}
 
     if(num_items > 0)