Pascal基本用法

 
var  
    x, y, max, num : integer;
    name : string;        {define a variable}
    const PI = 3.1415926; {define a constant}
begin
    assign(output, 'bbb.out'); {write output to file}
    reset(input);
    rewrite(output);

    {1. arithmetic operation}
    x := 10;
    y := 20;
    writeln('x + y = ', x + y); {free pascal not support IntToStr, but remeber to use in Delphi}
    writeln('x - y = ', x - y);
    writeln('x * y = ', x * y);
    writeln('x / y =1 ', x div y);

    writeln('x % y = ', x mod y);

    {2. relational operator and conditional operation}
    if x > y then
    begin
        max := x;
        writeln('x is large than y');
    end
    else if x = y then
    begin
        max := x;
        writeln('x is equals to y');
    end
    else begin
        max := y;
        writeln('x is less than y');
    end;

    writeln('max of x and y is : ', max);

    {3. boolean operator. If has more than one boolean operation in if, use () to surround each boolean operation.Otherwise, error will occur.}
    if (x=y) or (x<y) then
        writeln('x is less or equals y');

    {4. loop }
    num := 10; {attention: operation of assigning value shoud be put in begin statement other than var statement}
    writeln('======== while loop start =======');
    while num>0 do
    begin
        writeln('loop, num= ', num);
        num := num - 2;
    end; {attention: don't forget ';' after end}
    writeln('===== while loop end =====');

    writeln('======= for loop start ======');
    for num := 0 to 5 do
    begin
        writeln('loop, num= ', num);
    end;

    close(input);
    close(output);
end.

注意事项：

1) 变量及常量的定义需要放在var声明中，而变量的赋值操作必须放在begin下面

2) 程序中通过write、writeln输出内容，两种的区别是writeln输出内容后会回车换行

3) 如果使用Free Pascal IDE运行程序，运行之后界面一闪而过，这是因为程序运行较快，运行完成后又回到了

IDE界面。如果希望看到运行结果，可以在程序结束 添加 readln; 这样的话，程序运行之后会等待输入任意键，

输入完成后，才会回到IDE界面。也可以使用 Alt + F5 快捷键回到运行结果界面。另外，也可以使用输入输出流

将结果写入文件中，如下：

{begin下}
assign(input,'*.in');     {第二个参数为输入文件名，下行为输出文件名，因题而变}
assign(output,'*.out');
reset(input);
rewrite(output);

{业务代码}

close(input);
close(output);

4) if语句中如果有多个条件，则每个条件都要用括号括起来，不然会报错（应该是运算符优先级导致的，还没研究）

5) 开头的begin 需要 end. 与之对应，否则会报错： Syntax error, '.' expected but "end of file" found (Free Pascal中)