diff --git a/src/AMOEBA/amoeba_file.cpp b/src/AMOEBA/amoeba_file.cpp
index ebedbc13d5..2089ab3a27 100644
--- a/src/AMOEBA/amoeba_file.cpp
+++ b/src/AMOEBA/amoeba_file.cpp
@@ -416,7 +416,7 @@ void PairAmoeba::read_keyfile(char *filename)
 
     const auto words = Tokenizer(trimmed).as_vector();
     const int nwords = words.size();
-    const auto keyword = words[0];
+    const auto &keyword = words[0];
 
     if (utils::strmatch(keyword, "^[^a-z]+")) {
       ;    // ignore keywords that do not start with text
diff --git a/src/atom_vec_body.cpp b/src/atom_vec_body.cpp
index f2eef1d207..0726468c4f 100644
--- a/src/atom_vec_body.cpp
+++ b/src/atom_vec_body.cpp
@@ -118,7 +118,7 @@ void AtomVecBody::process_args(int narg, char **arg)
 #undef BODY_CLASS
 
   } else
-    error->all(FLERR, utils::check_packages_for_style("body", arg[0], lmp).c_str());
+    error->all(FLERR, utils::check_packages_for_style("body", arg[0], lmp));
 
   bptr->avec = this;
   icp = bptr->icp;
diff --git a/src/input.cpp b/src/input.cpp
index a641f300a3..09e5d6decb 100644
--- a/src/input.cpp
+++ b/src/input.cpp
@@ -212,7 +212,7 @@ void Input::file()
 
         mstart = m;
 
-        while (1) {
+        while (true) {
           if (maxline-m < 2) reallocate(line,maxline,0);
 
           // end of file reached, so break
@@ -437,18 +437,18 @@ void Input::parse()
     }
     if (*ptr == '\'') {
       ptrmatch = strchr(ptr+1,'\'');
-      if (ptrmatch == NULL)
+      if (ptrmatch == nullptr)
         error->all(FLERR,"Unmatched single quote in command");
       ptr = ptrmatch + 1;
     } else if (*ptr == '"') {
       if (strstr(ptr,"\"\"\"") == ptr) {
         ptrmatch = strstr(ptr+3,"\"\"\"");
-        if (ptrmatch == NULL)
+        if (ptrmatch == nullptr)
           error->all(FLERR,"Unmatched triple quote in command");
         ptr = ptrmatch + 3;
       } else {
         ptrmatch = strchr(ptr+1,'"');
-        if (ptrmatch == NULL)
+        if (ptrmatch == nullptr)
           error->all(FLERR,"Unmatched double quote in command");
         ptr = ptrmatch + 1;
       }
@@ -669,7 +669,7 @@ void Input::substitute(char *&str, char *&str2, int &max, int &max2, int flag)
 
     } else if (*ptr == '\'') {
       ptrmatch = strchr(ptr+1,'\'');
-      if (ptrmatch == NULL)
+      if (ptrmatch == nullptr)
         error->all(FLERR,"Unmatched single quote in command");
       nchars = ptrmatch+1 - ptr;
       strncpy(ptr2,ptr,nchars);
@@ -678,7 +678,7 @@ void Input::substitute(char *&str, char *&str2, int &max, int &max2, int flag)
     } else if (*ptr == '"') {
       if (strstr(ptr,"\"\"\"") == ptr) {
         ptrmatch = strstr(ptr+3,"\"\"\"");
-        if (ptrmatch == NULL)
+        if (ptrmatch == nullptr)
           error->all(FLERR,"Unmatched triple quote in command");
         nchars = ptrmatch+3 - ptr;
         strncpy(ptr2,ptr,nchars);
@@ -686,7 +686,7 @@ void Input::substitute(char *&str, char *&str2, int &max, int &max2, int flag)
         ptr2 += nchars;
       } else {
         ptrmatch = strchr(ptr+1,'"');
-        if (ptrmatch == NULL)
+        if (ptrmatch == nullptr)
           error->all(FLERR,"Unmatched double quote in command");
         nchars = ptrmatch+1 - ptr;
         strncpy(ptr2,ptr,nchars);