if语句
<p>语法：</p>
<pre><code class="language-delphi">if &lt;条件&gt; then
&lt;语句&gt;;</code></pre>
<p>或</p>
<pre><code class="language-delphi">if &lt;条件&gt; then
&lt;语句&gt; //不要分号
else
&lt;语句&gt;;
end;</code></pre>
<p>例1：按钮实现按一次，再按一次效果</p>
<pre><code class="language-delphi">procedure TForm1.Button1Click(Sender: TObject);
begin
if Button1.Tag = 0 then
begin
Button1.Caption:=&#039;Press again&#039;;
Button1.Tag:=1;
end else
begin
Button1.Caption:=&#039;Press&#039;;
Button1.Tag:=0;
end;
end; </code></pre>
<p>例2：显示上中下旬</p>
<pre><code class="language-delphi">procedure TForm1.Button1Click(Sender: TObject);
begin
if (Date&gt;=1) and (Date&lt;=10) then
ShowMessage(&#039;上旬&#039;)
else if (Date&gt;=11) and (Date&lt;=20) then
ShowMessage(&#039;中旬&#039;)
else if (Date&gt;=21) and (Date&lt;=31) then
ShowMessage(&#039;下旬&#039;)
else
ShowMessage(&#039;日期错误！&#039;);
end;</code></pre>