diff --git a/SConstruct b/SConstruct
index aaf15cc70..d15e32af9 100644
--- a/SConstruct
+++ b/SConstruct
@@ -60,8 +60,9 @@ for language, tools in languages_to_import.items():
 
 Export('env')
 
-env['CFLAGS'] = '-Wall -Wextra -Werror'
-env['CXXFLAGS'] = '-std=c++17'
+env['CCFLAGS'] = '-Wall -Wextra -Werror -pedantic'
+env['CFLAGS'] = '-std=gnu99'
+env['CXXFLAGS'] = '-std=c++17 -Wold-style-cast'
 env['ASFLAGS'] = '--64'
 env['COCONUTFLAGS'] = '--target 3.8'
 
diff --git a/contents/gaussian_elimination/code/cpp/gaussian_elimination.cpp b/contents/gaussian_elimination/code/cpp/gaussian_elimination.cpp
index 843392490..65d9ac6a8 100644
--- a/contents/gaussian_elimination/code/cpp/gaussian_elimination.cpp
+++ b/contents/gaussian_elimination/code/cpp/gaussian_elimination.cpp
@@ -73,10 +73,10 @@ std::vector<double> backSubs(const std::vector<std::vector<double> > &eqns) {
 
 
 void printMatrix(const std::vector<std::vector<double> > &matrix) {
-  for (int row = 0; row < matrix.size(); row++) {
+  for (std::size_t row = 0; row < matrix.size(); row++) {
     std::cout << "[";
 
-    for (int col = 0; col < matrix[row].size() - 1; col++)
+    for (std::size_t col = 0; col < matrix[row].size() - 1; col++)
       std::cout << std::setw(8) << std::fixed << std::setprecision(3)
                 << matrix[row][col];
 
diff --git a/contents/monte_carlo_integration/code/cpp/monte_carlo.cpp b/contents/monte_carlo_integration/code/cpp/monte_carlo.cpp
index f38d83f45..4a600d72e 100644
--- a/contents/monte_carlo_integration/code/cpp/monte_carlo.cpp
+++ b/contents/monte_carlo_integration/code/cpp/monte_carlo.cpp
@@ -37,8 +37,6 @@ double monte_carlo_pi(unsigned samples) {
 }
 
 int main() {
-    unsigned samples;
-
     double pi_estimate = monte_carlo_pi(10000000);
     std::cout << "Pi = " << pi_estimate << '\n';
     std::cout << "Percent error is: " << 100 * std::abs(pi_estimate - PI) / PI << " %\n";
diff --git a/contents/split-operator_method/code/cpp/split_op.cpp b/contents/split-operator_method/code/cpp/split_op.cpp
index 74f8df2b7..6ae20394e 100644
--- a/contents/split-operator_method/code/cpp/split_op.cpp
+++ b/contents/split-operator_method/code/cpp/split_op.cpp
@@ -97,7 +97,7 @@ void fft(vector_complex &x, bool inverse) {
 }
 
 void split_op(Params &par, Operators &opr) {
-    double density[opr.size];
+    auto density = std::vector<double>(opr.size, 0);
 
     for (size_t i = 0; i < par.timesteps; ++i) {
         for (size_t j = 0; j < opr.size; ++j) {
@@ -142,7 +142,7 @@ void split_op(Params &par, Operators &opr) {
         std::ofstream fstream = std::ofstream(filename_stream.str());
 
         if (fstream) {
-            for (int i = 0; i < opr.size; ++i) {
+            for (std::size_t i = 0; i < opr.size; ++i) {
                 std::stringstream data_stream;
 
                 data_stream << i << "\t" << density[i] << "\t" << real(opr.v[i]) << "\n";