Fixed executable permissions and added sample program

syscalls/Makefile

@@ -2,7 +2,7 @@ CFLAGS += -Wall -nostdlib -ffreestanding
 LDFLAGS += -nostdlib -ffreestanding
 CC = gcc
 
-ALL: cat grep hello ls pingpong counter shell sigtest testprint syserr
+ALL: cat grep hello ls pingpong counter shell sigtest testprint syserr factorial
 
 %.o: %.c
 	$(CC) $(CFLAGS) -c -o $@ $<

syscalls/ece391factorial.c

@@ -0,0 +1,44 @@
+#include <stdint.h>
+
+#include "ece391support.h"
+#include "ece391syscall.h"
+
+#define BUFSIZE 10
+
+int main ()
+{
+    uint8_t buf[BUFSIZE];
+    uint32_t cnt, i, num;
+
+    ece391_fdputs(1, (uint8_t*)"Enter number to calculate factorial of:\n");
+    if (-1 == (cnt = ece391_read(0, buf, BUFSIZE-1)) ) {
+        ece391_fdputs(1, (uint8_t*)"Can't read the number from keyboard.\n");
+     return 3;
+    }
+    buf[cnt] = '\0';
+
+    num = 0;
+    i = 0;
+    while (buf[i] >= '0' && buf[i] <= '9')
+    {
+        num *= 10;
+        num += (uint32_t)(buf[i] - '0');
+        i++;
+    }
+
+    cnt = 1;
+    while (num != 0)
+    {
+        cnt *= num;
+        num--;
+    }
+
+    uint8_t out[BUFSIZE];
+    ece391_itoa(cnt, out, 10);
+
+    ece391_fdputs(1, (uint8_t*)"Factorial: ");
+    ece391_fdputs(1, out);
+    ece391_fdputs(1, (uint8_t*)"\n");
+
+    return 0;
+}