Update result according to the operator
if ( opr == ' + ' ) : NEW_LINE INDENT res += value ( opd ) ; NEW_LINE DEDENT elif ( opr == ' - ' ) : NEW_LINE INDENT res -= int ( value ( opd ) ) ; NEW_LINE DEDENT elif ( opr == ' * ' ) : NEW_LINE INDENT res *= int ( value ( opd ) ) ; NEW_LINE DEDENT elif ( opr == ' / ' ) : NEW_LINE INDENT res /= int ( value ( opd ) ) ; NEW_LINE DEDENT