diff --git a/SCR3.1/TP4/helpers.c b/SCR3.1/TP4/helpers.c
new file mode 100644
index 0000000..718fe40
--- /dev/null
+++ b/SCR3.1/TP4/helpers.c
@@ -0,0 +1,19 @@
+#include "helpers.h"
+#include <signal.h>
+#include <time.h>
+
+int set_signal_handler(int signo, void (*handler)(int)) {
+    struct sigaction sa;
+    sa.sa_handler = handler;    // call `handler` on signal
+    sigemptyset(&sa.sa_mask);   // don't block other signals in handler
+    sa.sa_flags = SA_RESTART;            //  restart system calls
+    return sigaction(signo, &sa, NULL);
+}
+
+double tstamp(void) {                                                                                    
+	struct timespec tv;
+	clock_gettime(CLOCK_REALTIME, &tv);
+	return tv.tv_sec + tv.tv_nsec * 1.0e-9;
+}
+
+
diff --git a/SCR3.1/TP4/helpers.h b/SCR3.1/TP4/helpers.h
new file mode 100644
index 0000000..2084c6a
--- /dev/null
+++ b/SCR3.1/TP4/helpers.h
@@ -0,0 +1,7 @@
+#ifndef _HELPERS_H
+#define _HELPERS_H
+
+int set_signal_handler(int signo, void (*handler)(int));
+double tstamp(void);
+
+#endif
diff --git a/SCR3.1/TP4/pi.c b/SCR3.1/TP4/pi.c
new file mode 100644
index 0000000..5d2ceb3
--- /dev/null
+++ b/SCR3.1/TP4/pi.c
@@ -0,0 +1,59 @@
+#include<unistd.h>
+#include<stdio.h>
+#include<stdlib.h>
+#include<signal.h>
+#include<stdint.h>
+#include<assert.h>
+#include "helpers.h"
+#include "helpers.c"
+
+uint64_t shots = 0,
+		 shots_in = 0;
+
+double pi = 0, t1;
+
+void int_handler(int){
+	alarm(0);
+	char c;
+	printf("Le programme tourne depuis %f secondes, voulez-vous vraiment l'arrêter ? (O)ui / (N)on", tstamp() - t1);
+	c = getchar();
+	if (c == 'O' || c == 'o' || c == 'Y' || c == 'y'){
+		exit(0);
+	}
+	else{
+		return;
+		alarm(5);
+	}
+}
+
+void alarm_handler(int){
+	printf("Valeur de pi en cours = %f\n", pi);
+	printf("Nombre de tirs effectués = %f\n", (double) shots);
+	alarm(5);
+}
+
+void quit_handler(int){
+	alarm(0);
+	shots = 0;
+	shots_in = 0;
+	t1 = tstamp();
+	alarm(5);
+}
+
+int main(int argc,char * argv[])
+{
+	double x,y;
+	t1 = tstamp();
+	alarm(5);
+	set_signal_handler(SIGALRM, &alarm_handler);
+        set_signal_handler(SIGINT, &int_handler);	
+	set_signal_handler(SIGQUIT, &quit_handler); 
+	while(1){
+		x = ((double)rand())/(double)RAND_MAX;
+		y = ((double)rand())/(double)RAND_MAX;
+		shots ++;
+		if ((x*x+y*y) <= 1) 
+			shots_in ++;
+		pi = shots_in * 1.0 / shots * 4;
+	}
+}
diff --git a/SCR3.1/TP4/ping_pong.c b/SCR3.1/TP4/ping_pong.c
new file mode 100644
index 0000000..2ae839a
--- /dev/null
+++ b/SCR3.1/TP4/ping_pong.c
@@ -0,0 +1,58 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <errno.h>
+#include <assert.h>
+
+#define N 10000
+void sig_hand(int sig) {}
+
+sigset_t saveMask, blockMask;
+
+void player_wait(){
+	pause();
+}
+void child_process()
+{
+	int x = 0;
+	while(x < N)
+	{
+		player_wait();
+		printf("\tPong %d!\n", ++x);
+		kill(getppid(), SIGUSR1);
+	}
+	return ;
+}
+
+void parent_process(pid_t pid)
+{
+	int y = 0;
+	while (y < N)
+	{
+		printf("Ping %d!\n", ++y);
+		kill(pid, SIGUSR1);
+		player_wait();
+	}
+	return ;
+}
+
+int main(int argc, char* argv[])
+{
+	//set up signal handler for parent & child
+	struct sigaction sa;
+	sigemptyset(&sa.sa_mask);
+	sa.sa_flags = 0;
+	sa.sa_handler = sig_hand;
+
+	assert (sigaction(SIGUSR1, &sa, NULL) != -1);
+
+	pid_t pid = fork();
+
+	if (pid == 0)
+		child_process();
+	else
+		parent_process(pid);
+	return 0;
+}
diff --git a/SCR3.1/TP4/section_critique.c b/SCR3.1/TP4/section_critique.c
new file mode 100644
index 0000000..04725f4
--- /dev/null
+++ b/SCR3.1/TP4/section_critique.c
@@ -0,0 +1,34 @@
+#include<unistd.h>
+#include<stdio.h>
+#include<stdlib.h>
+#include<signal.h>
+#include<stdint.h>
+#include<assert.h>
+#include "helpers.h"
+
+
+int x=2,y=3;
+
+int swap(int *x,int *y)
+{
+	int tmp=*x;
+	*x=*y;
+	*y=tmp;
+}
+
+void sig_handler(int signo)
+{
+	switch(signo){
+		case SIGQUIT : 
+			printf("x=%d y=%d\n",x,y);
+			break;
+	}
+}
+
+int main(int argc,char * argv[])
+{
+	assert(set_signal_handler(SIGQUIT,sig_handler)==0);
+	while(1){
+		swap(&x,&y);
+	}
+}