Use a class or static variable which you can set each time through this code; something like:
private: System::Void btnMul_Click(System::Object^ sender, System::EventArgs^ e) {
static bool isMul = false;
if(isMul == false){
ice->(isMul, 8000, 6000); unsigned long data = 10;
unsigned long value;
value=5*data;
String^ str = value.ToString();
textBox1->Text=str;
isMul=true;
}
else
{
ice->(isMul, 8000, 6000); textBox1->Text = "";
isMul=false;
}