Eighth update on iterators - STACK

examples/stack/README.md

@@ -1,3 +1,4 @@
 # Stack examples
 
 * hanoi.c - Animated example of solving the hanoi tower.
+* iterator.c - A complete example of the stack iterator

examples/stack/hanoi.c

@@ -13,8 +13,6 @@
 
 STACK_GENERATE(s, stack, /* static */, int)
 
-#define MAX(a, b) a > b ? a : b
-
 void print_hanoi(stack *t1, stack *t2, stack *t3);
 const char *draw(int value);
 void move_disc(stack *from, stack *to);

examples/stack/iterator.c

@@ -0,0 +1,195 @@
+/**
+ * iterator.c
+ *
+ * Creation Date: 15/05/2019
+ *
+ * Authors:
+ * Leonardo Vencovsky (https://github.com/LeoVen)
+ *
+ * Iterator Example
+ */
+#include "stack.h"
+#include <stdio.h>
+#include <inttypes.h>
+
+// Creates a stack of integers
+STACK_GENERATE(s, stack, /* FMOD */, int)
+
+int main(int argc, char const *argv[])
+{
+    // Create a new stack with an initial capacity of 100
+    stack *my_stack = s_new(100);
+
+    // Add elements to the stack
+    for (int i = 0; i < 20; i++)
+    {
+        s_push(my_stack, i);
+    }
+
+    // Iterate from the start (top) to the end (bottom) of the stack
+    for (stack_iter it = my_stack->it_start(my_stack); // Initialize iterator 'it' to the start of the stack
+         !s_iter_end(&it);                             // Conditional stop (until it is not at the end)
+         s_iter_next(&it))                             // Iterator goes one position forward
+    {
+        // Access the current element
+        int e = s_iter_value(&it);
+
+        // Access the current index (index is relative to all the elements in the iteration)
+        size_t i = s_iter_index(&it);
+
+        // Print stack
+
+        // Index is useful in situations like this
+        // If it is the first element
+        if (i == 0)
+            printf("[ %d, ", e);
+        // If it is the last element
+        else if (i == s_count(my_stack) - 1)
+            printf("%d ]\n", e);
+        // For elements at the middle
+        else
+            printf("%d, ", e);
+    }
+
+    // Index can also be used to iterate over a certain portion of a collection
+    size_t limit = s_count(my_stack) / 2;
+    for (stack_iter it = my_stack->it_start(my_stack); !s_iter_end(&it); s_iter_next(&it))
+    {
+        // Access the current element
+        int e = s_iter_value(&it);
+
+        // Access the current index (index is relative to all the elements in the iteration)
+        size_t i = s_iter_index(&it);
+
+        // Print stack up until limit
+
+        // If it is the first element
+        if (i == 0)
+            printf("[ %d, ", e);
+        // If it is the last element
+        else if (i == limit - 1) // -1 because index is 0 based and we want half of the stack
+        {
+            printf("%d ]\n", e);
+            break;
+        }
+        // For elements at the middle
+        else
+            printf("%d, ", e);
+    }
+
+    // Going backwards
+    for (stack_iter it = my_stack->it_end(my_stack); // Initialize iterator 'it' to the end of the stack
+         !s_iter_start(&it);                         // Conditional stop (until it is not at the start)
+         s_iter_prev(&it))                           // Iterator goes one position backwards
+    {
+        // Access the current element
+        int e = s_iter_value(&it);
+
+        // Access the current index (index is relative to all the elements in the iteration)
+        size_t i = s_iter_index(&it);
+
+        // Print stack
+        // Note how the conditions for the first and last elements are simply swapped
+        // Because iterating backwards make the first element be the index count - 1
+        // and the last one be the index 0
+
+        // If it is the first element
+        if (i == s_count(my_stack) - 1)
+            printf("[ %d, ", e);
+        // If it is the last element
+        else if (i == 0)
+            printf("%d ]\n", e);
+        // For elements at the middle
+        else
+            printf("%d, ", e);
+    }
+
+    // You can also use iterators in a while loop
+    // But to do so you must declare the iterator struct outside the loop first
+    stack_iter it;
+
+    // You have three options:
+    // - Initialize it using the functions provided by the stack [ my_stack->it_start() and my_stack->it_end() ]
+    // - Initialize it using the init() function (when the iterator is already allocated)
+    // - Initialize it using the new() function (allocates on the heap, pointers only)
+
+    it = my_stack->it_start(my_stack);
+    it = my_stack->it_end(my_stack);
+
+    // This is equivalent to it_start()
+    s_iter_init(&it, my_stack);
+
+    // For pointers
+    // Also equivalent to it_start()
+    stack_iter *iter = s_iter_new(my_stack);
+
+    // The actual while loop
+    while (!s_iter_end(iter))
+    {
+        // Accessing elements
+        int e = s_iter_value(iter);
+        size_t i = s_iter_index(iter);
+
+        // Print index and element
+        printf("stack[%2" PRIuMAX "] = %2d\n", i, e);
+
+        // Move iterator forwards
+        s_iter_next(iter);
+    }
+
+    // Send the iterator to the start of the stack
+    s_iter_to_start(iter);
+
+    // Send the iterator to the end of the stack
+    s_iter_to_end(iter);
+
+    // Backwards loop
+    while (!s_iter_start(iter))
+    {
+        // Accessing elements
+        int e = s_iter_value(iter);
+        size_t i = s_iter_index(iter);
+
+        // Print index and element
+        printf("stack[%2" PRIuMAX "] = %2d\n", i, e);
+
+        // Move iterator backwards
+        s_iter_prev(iter);
+    }
+
+    // Certain iterators also allow you to modify the contents it is iterating over
+    // Exceptions are collections that depend of the current state of the element
+    // like tree-based collections and heap (collections that have some kind of ordering).
+    // You also can't change the keys of an associative collection
+
+    // Change every element that is divisible by 3 to the number 7
+    for (s_iter_to_start(&it); !s_iter_end(&it); s_iter_next(&it))
+    {
+        // Get a reference to the current value
+        int *r = s_iter_rvalue(&it);
+
+        if (r != NULL && *r % 3 == 0)
+            *r = 7;
+    }
+
+    // Now print it to see the difference
+    for (stack_iter it = my_stack->it_start(my_stack); !s_iter_end(&it); s_iter_next(&it))
+    {
+        int e = s_iter_value(&it);
+        size_t i = s_iter_index(&it);
+
+        if (i == 0)
+            printf("[ %d, ", e);
+        else if (i == s_count(my_stack) - 1)
+            printf("%d ]\n", e);
+        else
+            printf("%d, ", e);
+    }
+
+    // Dispose the iterator called by s_iter_new()
+    s_iter_free(iter);
+    // Dispose the stack created
+    s_free(my_stack);
+
+    return 0;
+}