Data update

Task/Gotchas/C/gotchas-1.c

@@ -1,3 +1,3 @@
-if(a=b){} //assigns to "a" the value of "b". Then, if "a" is nonzero, the code in the curly braces is run.
-
-if(a==b){} //runs the code in the curly braces if and only if the value of "a" equals the value of "b".
+if (a=b) {
+	...;	/* this is run if b is non-zero */
+}

Task/Gotchas/C/gotchas-10.c

@@ -1,7 +1,2 @@
-int main()
-{
-int x = 3;
-int y = 5;
-int z = 7;
-printf("%d %d %d %x %x",x,y,z);  //on an Intel cpu the first %x reveals %%ebp and the second reveals the return address.)
-}
+myArray[40];
+int x = gotcha(&myArray[0]);

Task/Gotchas/C/gotchas-11.c

@@ -1,3 +1,7 @@
-(let numbers [1 2 3 4]
-     maximum (max numbers)) ;should be (... max numbers)
-(+ maximum 5)
+int foo(char buf[],int length){}
+
+int main()
+{
+char myArray[30];
+int j = foo(myArray,sizeof(myArray)); //passes 30 as the length parameter.
+}

Task/Gotchas/C/gotchas-12.c

@@ -1,2 +1,4 @@
-(mock + (fn a b ((unmocked +) a b 1)))
-(+ 2 3)
+int x = 3;
+int y = 5;
+printf("%d %d %x\n",x,y);	/* this may crash or print undefined values after 3 5 */
+printf("testing %n\n");	/* this writes the int value 8 to an undefined location */

Task/Gotchas/C/gotchas-13.c

@@ -0,0 +1,7 @@
+void
+say_hello(const char *name)	/* assume name is something the user entered */
+{
+	printf("hello ");
+	printf(name);	/* the name entered could be "%s" or "%n" or something */
+	printf("\n");
+}

Task/Gotchas/C/gotchas-2.c

@@ -1 +1,3 @@
-int foo[4] = {4,8,12,16};
+if (a==b) {
+	...;	/* this is run if a and b are equal */
+}

Task/Gotchas/C/gotchas-3.c

@@ -1,4 +1,3 @@
-int foo[4] = {4,8,12,16};
-int x = foo[0];  //x = 4
-int y = foo[3];  //y = 16
-int z = foo[4];  //z = ?????????
+if ( (a=b) ) {	/* this shows that an assignment was intended */
+	...;
+}

Task/Gotchas/C/gotchas-4.c

@@ -1,5 +1 @@
-int foo()
-{
-char bar[20];
-return sizeof(bar);
-}
+int foo[4] = { 4, 8, 12, 16 };

Task/Gotchas/C/gotchas-5.c

@@ -1,7 +1,4 @@
-int foo()
-{
-#define size_of_bar 20  //the sizeof operator is the same as doing this essentially.
-
-char bar[size_of_bar];
-return size_of_bar;
-}
+int foo[4] = { 4, 8, 12, 16 };
+int x = foo[0];  /* x = 4 */
+int y = foo[3];  /* y = 16 */
+int z = foo[4];  /* z contains whatever was after foo[3] in memory */

Task/Gotchas/C/gotchas-6.c

@@ -1,4 +1,5 @@
-int gotcha(char bar[])
-{
-return sizeof(bar);
+int i;
+int squarenums[10];
+for (i=0; i<=10; i++) {
+	squarenums[i] = i * i;
 }

Task/Gotchas/C/gotchas-7.c

@@ -1,2 +1,5 @@
-myArray[40];
-int x = gotcha(myArray);
+int foo()
+{
+	char bar[20];
+	return sizeof(bar);	/* returns 20 as expected */
+}

Task/Gotchas/C/gotchas-8.c

@@ -1,2 +1,4 @@
-myArray[40];
-int x = gotcha(&myArray[0]);
+int gotcha(char bar[])	/* could have been: int gotcha(char *bar) */
+{
+	return sizeof(bar);	/* returns the size of a pointer to char, probably 4 on 32-bit systems and 8 on 64-bit systems */
+}

Task/Gotchas/C/gotchas-9.c

@@ -1,7 +1,2 @@
-int foo(char buf[],int length){}
-
-int main()
-{
-char myArray[30];
-int j = foo(myArray,sizeof(myArray)); //passes 30 as the length parameter.
-}
+char myArray[40];
+int x = gotcha(myArray);

Task/Gotchas/X86-Assembly/gotchas.x86

@@ -1,4 +1,15 @@
+; this takes two bytes, it is slower on some processors but faster or the same on others
 label:
-;loop body goes here
-DEC ECX
-JNZ label
+    loop label
+
+; this takes three bytes but is slower on some processors
+label:
+    dec ecx
+    jnz label
+
+; this is takes five bytes and is potentially faster than the above
+label:
+    sub ecx,1
+    jnz label
+
+; there is also a two-byte jecxz instruction but no jecxnz