Basic statements of the pasical program

Example calculates the area s of a circle with radius r

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code:program area;

const pi=;

var s,r:real;

beginreadln(r);

s:=pi*sqr(r);

writeln(’s=’,s);

end.The first line of the above procedure is called the program header. The content enclosed in curly braces (comments can be represented by or (*) is a comment, and the second line of the program is a comment, which has no effect on the compilation and operation of the program except for giving people to see and increasing the readability of the program. A program can contain multiple comments that appear in different places, or it may not have comments.

The third line of the program is the description of the constant, and the fourth line of the program is the description of the variables. The program from begin to end is the execution part of the (statement) aDescription section.

The description section is used to define and describe the data used in the program, and consists of a unit description, a label description, a constant description, a type description, a variable description, and a function or procedure description, and the data must be described in the order in which they are described. But a simple turbo pascal program can also be left without a description section, which means that the description section is optional.

b.Execution part.

The execution section describes what the program is going to do. It must start with a turbo pascal reserved word begin and end with the reserved word end followed by a period, with some utterances performing specific operations in between, and a semicolon as the separator between the utterances. begin and end must be in pairs, which is a must for a turbo pascal program.

A full stop immediately after the end indicates the end of the execution and also the end of the entire program. Any statement thereafter is invalid. Turbo Pascal stipulates that semicolons that appear immediately before END are allowed to be omitted.

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code:program;

uses a description of the known unit;

label description;

description of the const constant;

type;

description of var variables;

operator

operator description;

function

Function description; procedure

description of the process; begin

Statement; Statement;

Statement; end.

Primary, quadratic function trigonometric functions.