Add stack push, pop and peek

Also fixed various errors in the test file and is_stack_empty methods.

stack.c

@@ -15,19 +15,37 @@ void stack_init(stack *s, int size) {
 bool stack_is_empty(stack s) {
     bool is_empty = true;
 
+    if (s.top >= 0 && s.size >= 0 && s.data[0] >= 0) {
+        is_empty = false;
+    }
+
     return is_empty;
 }
 
+
 void stack_push(stack *s, int val) {
+    int next_top = s->top + 1;
 
+    // Push the value if the stack is not full
+    if (next_top < s->size && s->data[next_top] < 0) {
+        s->data[next_top] = val;
+        s->top = next_top;
+    }
 }
 
 void stack_pop(stack *s, int *val) {
-
+    if (s->top >= 0) {
+        *val = s->data[s->top];
+        s->data[s->top] = -1;
+        s->top -= 1;
+        s->size -= 1;
+    }
 }
 
 void stack_peek(stack s, int *val) {
-
+    if (s.size > 0) {
+        *val = s.data[s.top];
+    }
 }
 
 void stack_destroy(stack *s) {

test.c

@@ -18,7 +18,6 @@ void test_stack_init(stack *s, int size) {
 void test_stack_destroy(stack *s) {
     printf("Testing stack_destroy()...\n");
     stack_destroy(s);
-    // TODO: Verify if s is already null or not
     assert(s->data == NULL);
     assert(s->top == -1);
     printf("OK.\n");
@@ -40,7 +39,7 @@ void test_stack_peek(stack s, int *val) {
     printf("Testing stack_peek()...\n");
     stack_peek(s, val);
     // TODO: Verify test
-    assert(val == &s.top);
+    assert(*val == s.data[s.top]);
     printf("OK.\n");
 }
 
@@ -48,14 +47,14 @@ void test_stack_push(stack *s, int val) {
     printf("Testing stack_push()...\n");
     stack_push(s, val);
     // Testing push with remaining spaces
-    assert(s->top == val);
+    assert(s->data[s->top] == val);
     // Testing push on full stack
-    stack *stack_full;
+    stack stack_full;
     int value_top_full_stack_value = 100;
-    stack_init(stack_full, 1);
-    stack_push(stack_full, value_top_full_stack_value);
-    stack_push(stack_full, val);
-    assert(stack_full->top == value_top_full_stack_value);
+    stack_init(&stack_full, 1);
+    stack_push(&stack_full, value_top_full_stack_value);
+    stack_push(&stack_full, val);
+    assert(stack_full.data[stack_full.top] == value_top_full_stack_value);
     printf("OK.\n");
 }
 
@@ -67,13 +66,12 @@ void test_stack_pop(stack *s, int *val) {
         // Add a value if the stack is empty
         stack_push(s, 5);
     }
-    top_before_pop = s->top;
+    top_before_pop = s->data[s->top];
     stack_pop(s, val);
-    // TODO: Verify test
-    assert(val == &top_before_pop);
+    assert(*val == top_before_pop);
 
     // Clear the stack
-    while(s->size != 0) {
+    while(s->top >= 0) {
         stack_pop(s, val);
     }
     // Test pop when stack is empty
@@ -87,7 +85,7 @@ void test_stack_pop(stack *s, int *val) {
 int main() {
     stack s, non_empty_stack;
     int size = 10, value_to_add = 7;
-    int *val;
+    int val;
     printf("Starting the tests...\n");
     // Test init and destroy
     test_stack_init(&s, size);
@@ -97,14 +95,14 @@ int main() {
     stack_init(&s, size);
     stack_init(&non_empty_stack, 3);
     non_empty_stack.data[0] = 1;
-    non_empty_stack.top = non_empty_stack.data[0];
+    non_empty_stack.top = 0;
 
     // Test the other functions
     test_stack_is_empty(&s);
     test_stack_is_not_empty(&non_empty_stack);
-    test_stack_peek(s, val);
+    test_stack_peek(s, &val);
     test_stack_push(&s, value_to_add);
-    test_stack_pop(&s, val);
+    test_stack_pop(&s, &val);
 
     // Free the memory
     stack_destroy(&s);