support spawning dmenu with more than 10 monitors

config.def.h

@@ -57,7 +57,7 @@ static const Layout layouts[] = {
 #define SHCMD(cmd) { .v = (const char*[]){ "/bin/sh", "-c", cmd, NULL } }
 
 /* commands */
-static char dmenumon[2] = "0"; /* component of dmenucmd, manipulated in spawn() */
+static char dmenumon[8]; /* component of dmenucmd, manipulated in spawn() */
 static const char *dmenucmd[] = { "dmenu_run", "-m", dmenumon, "-fn", dmenufont, "-nb", col_gray1, "-nf", col_gray3, "-sb", col_cyan, "-sf", col_gray4, NULL };
 static const char *termcmd[]  = { "st", NULL };
 

dwm.c

@@ -1657,7 +1657,7 @@ spawn(const Arg *arg)
 	pid_t pid;
 
 	if (arg->v == dmenucmd)
-		dmenumon[0] = '0' + selmon->num;
+		snprintf(dmenumon, sizeof(dmenumon), "%d", selmon->num);
 
 	if ((pid = fork()) == -1) {
 		fprintf(stderr, "dwm: fork failed: %s\n", strerror(errno));