//Declaration of struct "stack"
//INV: FILO - "First in - last out"
typedef struct {
    int* arrayOfIntegers;
    int size;
} stack;

//Creating instance of struct "stack"
stack* createStack(size_t size) {
    stack *newStack = calloc(1, sizeof(stack));
    newStack -> arrayOfIntegers = (int*)calloc(size, sizeof(int));
    newStack -> size = 0;
    return newStack;
}

void ensureCapacityOfStack(stack* stack) {
    int* newArray = (int*)calloc(2 * (size_t)stack -> size, sizeof(int));
    memcpy(newArray, stack -> arrayOfIntegers, stack -> size);
    stack -> arrayOfIntegers = newArray;
}

void ensureCapacity(char* expression, size_t size) {
    char* newLine = (char*)calloc(2 * size + 1, sizeof(char));
    memcpy(newLine, expression, size);
    expression = newLine;
}

//Add the element to stack                                                                  Time: O(1)
void push(stack* stack, int value) {
    stack -> arrayOfIntegers[stack -> size++] = value;
    if (stack -> size % 1000 == 0) {
        ensureCapacityOfStack(stack);
    }
}

//Returns the element on the peek of stack                                                  Time: O(1)
int peek(stack* stack) {
    return stack -> arrayOfIntegers[stack -> size - 1];
}

//Delete the peek element from stack                                                        Time: O(1)
void pop(stack* stack) {
    if (stack -> size == 0) {
        printf("bad input");
        exit(1);
    }
    stack -> arrayOfIntegers[stack -> size--] = 0;
}