step-3-compile-error.c

/* main.c */

printf("At the top of the stack is `%d`\n\n", stack->top->value);

// Output from the compiler:
main.c:11:61: error: incomplete definition of type 'struct int_node'
    printf("At the top of the stack is `%d`\n\n", stack->top->value);
                                                  ~~~~~~~~~~^
./int_stack.h:6:16: note: forward declaration of 'struct int_node'
typedef struct int_node IntNode;
               ^