STYLE: use string substr instead of string::operator()

- makes the purpose clearer.
  In some places, string::resize() is even simpler.

- use C++11 string::back() in preference to str[str.size()-1]

applications/utilities/mesh/conversion/fluent3DMeshToFoam/fluent3DMeshToFoam.L

@@ -221,6 +221,7 @@ redundantBlock             {space}({comment}|{unknownPeriodicFace}|{periodicFace
 endOfSection               {space}")"{space}
 
 
+/* balance "-quoted for editor */
 
  /* ------------------------------------------------------------------------ *\
                       -----  Exclusive start states -----
@@ -693,7 +694,7 @@ endOfSection               {space}")"{space}
 {lbrac}{label} {
         Warning
             << "Found unknown block of type: "
-            << Foam::string(YYText())(1, YYLeng()-1) << nl
+            << std::string(YYText()).substr(1, YYLeng()-1) << nl
             << "    on line " << lineNo << endl;
 
         yy_push_state(ignoreBlock);

applications/utilities/mesh/manipulation/setSet/setSet.C

@@ -903,10 +903,10 @@ int main(int argc, char *argv[])
             }
 
             // Strip off anything after #
-            string::size_type i = rawLine.find_first_of("#");
+            string::size_type i = rawLine.find('#');
             if (i != string::npos)
             {
-                rawLine = rawLine(0, i);
+                rawLine.resize(i);
             }
 
             if (rawLine.empty())

applications/utilities/preProcessing/changeDictionary/changeDictionary.C

@@ -254,7 +254,7 @@ bool merge
 
         if (key[0] == '~')
         {
-            word eraseKey = key(1, key.size()-1);
+            const word eraseKey = key.substr(1);
             if (thisDict.remove(eraseKey))
             {
                 // Mark thisDict entry as having been match for wildcard
@@ -325,7 +325,7 @@ bool merge
 
             if (key[0] == '~')
             {
-                word eraseKey = key(1, key.size()-1);
+                const word eraseKey = key.substr(1);
 
                 // List of indices into thisKeys
                 labelList matches