怪异的php语法,求解！

看下面的语句：

echo "A1: ".(strpos("csd","c"))."
";
echo "A2: ".(strpos("csd","c")>=0)."
";
echo "B1: ".(strpos("csd","h",0))."
";
echo "B2: ".(strpos("csd","h",0)>=0)."
";

if(strpos("abc","a")>=0)
{
echo "a in abc"."
";
}
else
{
echo "a not in abc"."
";
}

if(strpos("abc","u")>=0)
{
echo "u in abc"."
";
}
else
{
echo "u not in abc"."
";
}

if(strpos("a","abc")>=0)
{
echo "abc in a"."
";
}
else
{
echo "abc not in a"."
";
}

if(strpos("u","abc")>=0)
{
echo "abc in u"."
";
}
else
{
echo "abc not in u"."
";
}

strpos

//显示的结果

A1: 0
A2: 1
B1:
B2: 1
a in abc
u in abc
abc in a
abc in u

定义和用法

strpos() 函数返回字符串在另一个字符串中第一次出现的位置。

如果没有找到该字符串，则返回 false。

语法

strpos(string,find,start)

请教，在这里，比如我要判断 字符串"abc" 里包含 "a", 用哪个方法比较好呢?