today

week-047.md

@@ -178,3 +178,80 @@ void hit(struct alive *a, struct alive *b){
 ## [DAY-346] machine code
 
 > for few days we were playing the 4719 game https://punkx.org/4917/ every day we did a couple of cards, disassembling them and then assembling them and running them on paper
+
+
+## [DAY-347] machine code; pointers
+
+
+I made a lot of examples using the 27th card, and then also showed examples in C, and made some other cards on paper about dereferencing pointers
+
+```
+#    0 halt
+#    1 add R0 = R0 + R1, 2 subtract R0 = R0 - R1
+#    3 inc R0, 4 inc R1
+#    5 dec R0, 6 dec R1
+#    7 ring bell
+#  8 X print X
+#  9 X R0 = mem[X]
+# 10 X R1 = mem[X]
+# 11 X mem[X] = R0
+# 12 X mem[X] = R1
+# 13 X jump to address X
+# 14 X jump to address X if R0 == 0
+# 15 X jump to address X if R0 != 0
+#
+# *p++
+┌────────┐ ┌────────┐
+│ IP:  0 │ │ IS:  0 │
+└────────┘ └────────┘
+┌────────┐ ┌────────┐
+│ R0:  0 │ │ R1:  0 │
+└────────┘ └────────┘
+
+┌────┬────┬────┬────┐
+│  9 │ 12 │ 11 │  7 │
+├────┼────┼────┼────┤
+│ 11 │ 10 │  9 │  0 │
+├────┼────┼────┼────┤
+│  3 │ 11 │  0 │  0 │
+├────┼────┼────┼────┤
+│ 15 │  0 │  0 │  6 │
+└────┴────┴────┴────┘
+```
+
+examples:
+
+```
+#include <stdio.h>
+int main(void) {
+  int x = 7;
+  int* p = &x;
+  *p++;
+
+  printf("%d\n",x)
+  
+  return 0;
+}
+
+#include <stdio.h>
+int main(void) {
+  int x = 7;
+  int* p = &x;
+  *p = 3;
+
+  printf("%d\n",x)
+  
+  return 0;
+}
+
+#include <stdio.h>
+int main(void) {
+  int x = 7;
+  
+  scanf("%d",&x);
+
+  printf("%d\n",x);
+  
+  return 0;
+}
+```