diff --git a/01_accelQuery/configure.ac b/01_accelQuery/configure.ac
index 1704676..04518ba 100644
--- a/01_accelQuery/configure.ac
+++ b/01_accelQuery/configure.ac
@@ -23,10 +23,10 @@ fi
 ##############################################################################80
 AC_PROG_CC([clang gcc])
 AS_IF([test "${CC}" = gcc],
-  [CFLAGS="-Wall -fopenmp -foffload=nvptx-none -I${CUDAINC} $CFLAGS"
+  [CFLAGS="-Wall -O2 -fopenmp -foffload=nvptx-none -I${CUDAINC} $CFLAGS"
    LDFLAGS="-L${CUDALIB} $LDFLAGS"])
 AS_IF([test "${CC}" = clang],
-  [CFLAGS="-Wall -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -I${CUDAINC} \
+  [CFLAGS="-Wall -O2 -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -I${CUDAINC} \
    -Xopenmp-target -march=sm_61 $CFLAGS"
    LDFLAGS="-L${CUDALIB} $LDFLAGS"])
 ##############################################################################80
diff --git a/01_accelQuery/src/prtAccelInfo.c b/01_accelQuery/src/prtAccelInfo.c
index f11dce1..0807275 100644
--- a/01_accelQuery/src/prtAccelInfo.c
+++ b/01_accelQuery/src/prtAccelInfo.c
@@ -9,10 +9,6 @@
  * @copyright CC BY-SA 2.0
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <cuda_runtime.h>
@@ -94,7 +90,3 @@ void prtAccelInfo(int iaccel)
   printf("warp size                : %d\n", dev.warpSize);
   printf("============================================================\n");
 }
-
-#ifdef __cplusplus
-}
-#endif
diff --git a/02_dataTransRate/configure.ac b/02_dataTransRate/configure.ac
index 82b0baa..befe143 100644
--- a/02_dataTransRate/configure.ac
+++ b/02_dataTransRate/configure.ac
@@ -23,10 +23,10 @@ fi
 ##############################################################################80
 AC_PROG_CC([clang gcc])
 AS_IF([test "${CC}" = gcc],
-  [CFLAGS="-Wall -fopenmp -foffload=nvptx-none -I${CUDAINC} $CFLAGS"
+  [CFLAGS="-Wall -O2 -fopenmp -foffload=nvptx-none -I${CUDAINC} $CFLAGS"
    LDFLAGS="-L${CUDALIB} $LDFLAGS"])
 AS_IF([test "${CC}" = clang],
-  [CFLAGS="-Wall -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -I${CUDAINC} \
+  [CFLAGS="-Wall -O2 -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -I${CUDAINC} \
    -Xopenmp-target -march=sm_61 $CFLAGS"
    LDFLAGS="-L${CUDALIB} $LDFLAGS"])
 ##############################################################################80
diff --git a/02_dataTransRate/src/check1ns.c b/02_dataTransRate/src/check1ns.c
index daf8eee..c01f906 100644
--- a/02_dataTransRate/src/check1ns.c
+++ b/02_dataTransRate/src/check1ns.c
@@ -10,10 +10,6 @@
  * @copyright CC BY-SA 2.0
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -30,7 +26,3 @@ void check1ns(void)
   }
   assert(1l == res.tv_nsec);
 }
-
-#ifdef __cplusplus
-}
-#endif
diff --git a/03_taskwait/configure.ac b/03_taskwait/configure.ac
index 762b1a1..5657924 100644
--- a/03_taskwait/configure.ac
+++ b/03_taskwait/configure.ac
@@ -23,10 +23,10 @@ fi
 ##############################################################################80
 AC_PROG_CC([clang gcc])
 AS_IF([test "${CC}" = gcc],
-  [CFLAGS="-Wall -fopenmp -foffload=nvptx-none -I${CUDAINC} $CFLAGS"
+  [CFLAGS="-Wall -O2 -fopenmp -foffload=nvptx-none -I${CUDAINC} $CFLAGS"
    LDFLAGS="-L${CUDALIB} $LDFLAGS"])
 AS_IF([test "${CC}" = clang],
-  [CFLAGS="-Wall -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -I${CUDAINC} \
+  [CFLAGS="-Wall -O2 -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -I${CUDAINC} \
    -Xopenmp-target -march=sm_61 $CFLAGS"
    LDFLAGS="-L${CUDALIB} $LDFLAGS"])
 ##############################################################################80
diff --git a/04_scalarAddition/configure.ac b/04_scalarAddition/configure.ac
index bbbcfa2..a1d3ec6 100644
--- a/04_scalarAddition/configure.ac
+++ b/04_scalarAddition/configure.ac
@@ -23,10 +23,10 @@ fi
 ##############################################################################80
 AC_PROG_CC([clang gcc])
 AS_IF([test "${CC}" = gcc],
-  [CFLAGS="-Wall -fopenmp -foffload=nvptx-none -I${CUDAINC} $CFLAGS"
+  [CFLAGS="-Wall -O2 -fopenmp -foffload=nvptx-none -I${CUDAINC} $CFLAGS"
    LDFLAGS="-L${CUDALIB} $LDFLAGS"])
 AS_IF([test "${CC}" = clang],
-  [CFLAGS="-Wall -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -I${CUDAINC} \
+  [CFLAGS="-Wall -O2 -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -I${CUDAINC} \
    -Xopenmp-target -march=sm_61 $CFLAGS"
    LDFLAGS="-L${CUDALIB} $LDFLAGS"])
 ##############################################################################80
diff --git a/04_scalarAddition/src/check1ns.c b/04_scalarAddition/src/check1ns.c
index daf8eee..c01f906 100644
--- a/04_scalarAddition/src/check1ns.c
+++ b/04_scalarAddition/src/check1ns.c
@@ -10,10 +10,6 @@
  * @copyright CC BY-SA 2.0
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -30,7 +26,3 @@ void check1ns(void)
   }
   assert(1l == res.tv_nsec);
 }
-
-#ifdef __cplusplus
-}
-#endif
diff --git a/05_saxpy/configure.ac b/05_saxpy/configure.ac
index 2075c61..d16246a 100644
--- a/05_saxpy/configure.ac
+++ b/05_saxpy/configure.ac
@@ -39,9 +39,9 @@ LDFLAGS+="-L${CUDALIB} -L${MKLLIB}"
 #
 AC_PROG_CC([clang gcc])
 AS_IF([test "${CC}" = gcc],
-  [CFLAGS="-Wall -fopenmp -foffload=nvptx-none $CFLAGS"])
+  [CFLAGS="-Wall -O2 -fopenmp -foffload=nvptx-none $CFLAGS"])
 AS_IF([test "${CC}" = clang],
-  [CFLAGS="-Wall -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda \
+  [CFLAGS="-Wall -O2 -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda \
            -Xopenmp-target -march=sm_61 $CFLAGS"])
 ##############################################################################80
 #
diff --git a/05_saxpy/src/asaxpy.c b/05_saxpy/src/asaxpy.c
index 0a05ccf..eeb21bb 100644
--- a/05_saxpy/src/asaxpy.c
+++ b/05_saxpy/src/asaxpy.c
@@ -17,10 +17,6 @@
  * @copyright CC BY-SA 2.0
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
@@ -267,7 +263,3 @@ for (int i = 0; i < m; ++i) {
     wtcalc += (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
   }
 }
-
-#ifdef __cplusplus
-}
-#endif
diff --git a/05_saxpy/src/check1ns.c b/05_saxpy/src/check1ns.c
index daf8eee..c01f906 100644
--- a/05_saxpy/src/check1ns.c
+++ b/05_saxpy/src/check1ns.c
@@ -10,10 +10,6 @@
  * @copyright CC BY-SA 2.0
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -30,7 +26,3 @@ void check1ns(void)
   }
   assert(1l == res.tv_nsec);
 }
-
-#ifdef __cplusplus
-}
-#endif
diff --git a/05_saxpy/src/hsaxpy.c b/05_saxpy/src/hsaxpy.c
index 22bab18..5603ae9 100644
--- a/05_saxpy/src/hsaxpy.c
+++ b/05_saxpy/src/hsaxpy.c
@@ -17,10 +17,6 @@
  * @copyright CC BY-SA 2.0
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <time.h>
 #ifdef _OPENMP
 #include <omp.h>
@@ -63,7 +59,3 @@ clock_gettime(CLOCK_REALTIME, rt + 1);
     wtcalc += (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
   }
 }
-
-#ifdef __cplusplus
-}
-#endif
diff --git a/05_saxpy/src/wtcalc.c b/05_saxpy/src/wtcalc.c
index bb00340..52385de 100644
--- a/05_saxpy/src/wtcalc.c
+++ b/05_saxpy/src/wtcalc.c
@@ -8,14 +8,6 @@
  * @copyright CC BY-SA 2.0
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include "wtcalc.h"
 
 double wtcalc;
-
-#ifdef __cplusplus
-}
-#endif
diff --git a/08_distThreads/configure.ac b/08_distThreads/configure.ac
index 9737e23..fce9ef6 100644
--- a/08_distThreads/configure.ac
+++ b/08_distThreads/configure.ac
@@ -23,10 +23,10 @@ fi
 ##############################################################################80
 AC_PROG_CC([clang gcc])
 AS_IF([test "${CC}" = gcc],
-  [CFLAGS="-Wall -fopenmp -foffload=nvptx-none -I${CUDAINC} $CFLAGS"
+  [CFLAGS="-Wall -O2 -fopenmp -foffload=nvptx-none -I${CUDAINC} $CFLAGS"
    LDFLAGS="-L${CUDALIB} $LDFLAGS"])
 AS_IF([test "${CC}" = clang],
-  [CFLAGS="-Wall -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -I${CUDAINC} \
+  [CFLAGS="-Wall -O2 -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -I${CUDAINC} \
    -Xopenmp-target -march=sm_61 $CFLAGS"
    LDFLAGS="-L${CUDALIB} $LDFLAGS"])
 ##############################################################################80
diff --git a/08_distThreads/src/gpuThreads.c b/08_distThreads/src/gpuThreads.c
index 2b462a8..3e1971b 100644
--- a/08_distThreads/src/gpuThreads.c
+++ b/08_distThreads/src/gpuThreads.c
@@ -9,10 +9,6 @@
  * @copyright CC BY-SA 2.0
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdio.h>
 #include <stdlib.h>
 #ifdef _OPENMP
@@ -415,7 +411,3 @@ void gpuThreads(int i)
    */
   free(league);
 }
-
-#ifdef __cplusplus
-}
-#endif
diff --git a/09_matAdd/configure.ac b/09_matAdd/configure.ac
index 4e5dad3..bcca20e 100644
--- a/09_matAdd/configure.ac
+++ b/09_matAdd/configure.ac
@@ -39,9 +39,9 @@ LDFLAGS+="-L${CUDALIB} -L${MKLLIB}"
 #
 AC_PROG_CC([clang gcc])
 AS_IF([test "${CC}" = gcc],
-  [CFLAGS="-Wall -fopenmp -foffload=nvptx-none $CFLAGS"])
+  [CFLAGS="-Wall -O2 -fopenmp -foffload=nvptx-none $CFLAGS"])
 AS_IF([test "${CC}" = clang],
-  [CFLAGS="-Wall -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda \
+  [CFLAGS="-Wall -O2 -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda \
            -Xopenmp-target -march=sm_61 $CFLAGS"])
 ##############################################################################80
 #
diff --git a/09_matAdd/src/matAddAB.c b/09_matAdd/src/matAddAB.c
index 08eb26d..d580f7c 100644
--- a/09_matAdd/src/matAddAB.c
+++ b/09_matAdd/src/matAddAB.c
@@ -11,10 +11,6 @@
  * @copyright CC BY-SA 2.0
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
@@ -299,7 +295,3 @@ for (int i = iblk * NTHRDS8;
     wtcalc += (rt[1].tv_sec - rt[0].tv_sec) + 1.0e-9 * (rt[1].tv_nsec - rt[0].tv_nsec);
   }
 }
-
-#ifdef __cplusplus
-}
-#endif