Fix some trivial compilation warnings

src/graph/generation/graph_complete.hh

@@ -31,12 +31,12 @@ struct get_complete
     template <class Graph>
     void operator()(Graph& g, size_t N, bool directed, bool self_loops) const
     {
-        for (int i = 0; i < N; ++i)
+        for (size_t i = 0; i < N; ++i)
             add_vertex(g);
 
-        for (int i = 0; i < N; ++i)
+        for (size_t i = 0; i < N; ++i)
         {
-            for (int j = directed ? 0 : i; j < N; ++j)
+            for (size_t j = directed ? 0 : i; j < N; ++j)
             {
                 if (!self_loops && j == i)
                     continue;
@@ -53,12 +53,12 @@ struct get_circular
     void operator()(Graph& g, size_t N, size_t k, bool directed,
                     bool self_loops) const
     {
-        for (int i = 0; i < N; ++i)
+        for (size_t i = 0; i < N; ++i)
             add_vertex(g);
 
-        for (int i = 0; i < N; ++i)
+        for (size_t i = 0; i < N; ++i)
         {
-            for (int j = i; j < i + k + 1; ++j)
+            for (size_t j = i; j < i + k + 1; ++j)
             {
                 if (!self_loops && j == i)
                     continue;

src/graph/layout/graph_radial.cc

@@ -99,7 +99,7 @@ struct do_get_radial
                     vertex_t w = target(*e, g);
                     new_layer.push_back(w);
 
-                    if (layers.size() - 1 == level[w])
+                    if (int(layers.size()) - 1 == level[w])
                         last = false;
                 }
                 if (out_degree(v, g) == 0)

src/graph/numpy_bind.hh

@@ -154,7 +154,7 @@ public:
                                const StrideList& strides)
         :base_t(data, sizes)
     {
-        for (int i = 0; i < dim; ++i)
+        for (size_t i = 0; i < dim; ++i)
             base_t::stride_list_[i] = strides[i];
     }
 };
@@ -191,7 +191,7 @@ boost::multi_array_ref<ValueType,dim> get_array(boost::python::object points)
     }
 
     vector<size_t> shape(dim);
-    for (int i = 0; i < dim; ++i)
+    for (size_t i = 0; i < dim; ++i)
         shape[i] =  PyArray_DIMS(pa)[i];
 
     vector<size_t> stride(dim);