Solution Review: Implement Stack Data Structure

package main
import (
	"fmt"
	"strconv"
)
const LIMIT = 4 // DONOT CHANGE IT!
type Stack struct {
	ix   int // first free position, so data[ix] == 0
	data [LIMIT]int
}
func (st *Stack) Push(n int) {
	if st.ix == LIMIT {	
		return // stack is full!
	}
	st.data[st.ix] = n
	st.ix++		// increment total no. of elements present
}
func (st *Stack) Pop() int {
	if st.ix >0{	// if stack not empty
		st.ix--		// decrease amount of elements present
		element := st.data[st.ix]
		st.data[st.ix] = 0
		return element
	}
	return -1	// if stack already empty
}
func (st Stack) String() string {
	str := ""
	for ix := 0; ix < st.ix; ix++ {
		str += "[" + strconv.Itoa(ix) + ":" + strconv.Itoa(st.data[ix]) + "]"
	}
	return str
}
func main() {
	st1 := new(Stack)
	fmt.Printf("%v\n", st1)
	st1.Push(3)	// function call to Push
	fmt.Printf("%v\n", st1)
	st1.Push(7) // function call to Push
	fmt.Printf("%v\n", st1)
	st1.Push(10) // function call to Push
	fmt.Printf("%v\n", st1)
	st1.Push(99) // function call to Push
	fmt.Printf("%v\n", st1)
	p := st1.Pop() // function call to Pop
	fmt.Printf("Popped %d\n", p)
	fmt.Printf("%v\n", st1)
	p = st1.Pop() // function call to Pop
	fmt.Printf("Popped %d\n", p)
	fmt.Printf("%v\n", st1)
	p = st1.Pop() // function call to Pop
	fmt.Printf("Popped %d\n", p)
	fmt.Printf("%v\n", st1)
	p = st1.Pop() // function call to Pop
	fmt.Printf("Popped %d\n", p)
	fmt.Printf("%v\n", st1)
}