Difference between revisions of "Basic Pascal Tutorial/Chapter 1/Assignment and Operations"
(New page: 1E - Assignment and Operations (author: Tao Yue, state: unchanged) Once you have declared a variable, you can store values in it. This is called assignment. To assign a value to a variab...) |
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To assign a value to a variable, follow this syntax: | To assign a value to a variable, follow this syntax: | ||
− | + | <delphi> | |
− | + | variable_name := expression; | |
+ | </delphi> | ||
Note that unlike other languages, whose assignment operator is just an equals sign, Pascal uses a colon followed by an equals sign, similarly to how it's done in most computer algebra systems. | Note that unlike other languages, whose assignment operator is just an equals sign, Pascal uses a colon followed by an equals sign, similarly to how it's done in most computer algebra systems. | ||
The expression can either be a single value: | The expression can either be a single value: | ||
− | + | <delphi> | |
− | + | some_real := 385.385837; | |
+ | </delphi> | ||
or it can be an arithmetic sequence: | or it can be an arithmetic sequence: | ||
− | + | <delphi> | |
− | + | some_real := 37573.5 * 37593 + 385.8 / 367.1; | |
+ | </delphi> | ||
The arithmetic operators in Pascal are: | The arithmetic operators in Pascal are: | ||
{| style="background-color:#f5f5f5" cellspacing=5 | {| style="background-color:#f5f5f5" cellspacing=5 | ||
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Each variable can only be assigned a value that is of the same data type. Thus, you cannot assign a real value to an integer variable. However, certain data types will convert to a higher data type. This is most often done when assigning integer values to real variables. Suppose you had this variable declaration section: | Each variable can only be assigned a value that is of the same data type. Thus, you cannot assign a real value to an integer variable. However, certain data types will convert to a higher data type. This is most often done when assigning integer values to real variables. Suppose you had this variable declaration section: | ||
− | + | <delphi> | |
− | + | var | |
− | + | some_int : integer; | |
− | + | some_real : real; | |
− | + | </delphi> | |
When the following block of statements executes, | When the following block of statements executes, | ||
− | + | <delphi> | |
− | + | some_int := 375; | |
− | + | some_real := some_int; | |
+ | </delphi> | ||
<tt>some_real</tt> will have a value of <tt>375.0</tt>. | <tt>some_real</tt> will have a value of <tt>375.0</tt>. | ||
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Do not attempt to use two operators side by side, like in: | Do not attempt to use two operators side by side, like in: | ||
− | + | <delphi> | |
+ | some_real := 37.5 * -2; | ||
+ | </delphi> | ||
This may make perfect sense to you, since you're trying to multiply by negative-2. However, Pascal will be confused — it won't know whether to multiply or subtract. You can avoid this by using parentheses to clarify: | This may make perfect sense to you, since you're trying to multiply by negative-2. However, Pascal will be confused — it won't know whether to multiply or subtract. You can avoid this by using parentheses to clarify: | ||
− | + | <delphi> | |
+ | some_real := 37.5 * (-2); | ||
+ | </delphi> | ||
The computer follows an order of operations similar to the one that you follow when you do arithmetic. Multiplication and division (<tt>* / div mod</tt>) come before addition and subtraction (<tt>+ -</tt>), and parentheses always take precedence. So, for example, the value of: <tt>3.5*(2+3)</tt> will be <tt>17.5.</tt> | The computer follows an order of operations similar to the one that you follow when you do arithmetic. Multiplication and division (<tt>* / div mod</tt>) come before addition and subtraction (<tt>+ -</tt>), and parentheses always take precedence. So, for example, the value of: <tt>3.5*(2+3)</tt> will be <tt>17.5.</tt> |
Revision as of 14:54, 5 January 2010
1E - Assignment and Operations (author: Tao Yue, state: unchanged)
Once you have declared a variable, you can store values in it. This is called assignment.
To assign a value to a variable, follow this syntax: <delphi> variable_name := expression; </delphi> Note that unlike other languages, whose assignment operator is just an equals sign, Pascal uses a colon followed by an equals sign, similarly to how it's done in most computer algebra systems.
The expression can either be a single value: <delphi> some_real := 385.385837; </delphi> or it can be an arithmetic sequence: <delphi> some_real := 37573.5 * 37593 + 385.8 / 367.1; </delphi> The arithmetic operators in Pascal are:
Operator | Operation | Operands | Result |
---|---|---|---|
+ | Addition or unary positive | real or integer | real or integer |
- | Subtraction or unary negative | real or integer | real or integer |
* | Multiplication | real or integer | real or integer |
/ | Real division | real or integer | real |
div | Integer division | integer | integer |
mod | Modulus (remainder division) | integer | integer |
div and mod only work on integers. / works on both reals and integers but will always yield a real answer. The other operations work on both reals and integers. When mixing integers and reals, the result will always be a real since data loss would result otherwise. This is why Pascal uses two different operations for division and integer division. 7 / 2 = 3.5 (real), but 7 div 2 = 3 (and 7 mod 2 = 1 since that's the remainder).
Each variable can only be assigned a value that is of the same data type. Thus, you cannot assign a real value to an integer variable. However, certain data types will convert to a higher data type. This is most often done when assigning integer values to real variables. Suppose you had this variable declaration section: <delphi> var
some_int : integer; some_real : real;
</delphi> When the following block of statements executes, <delphi> some_int := 375; some_real := some_int; </delphi> some_real will have a value of 375.0.
Changing one data type to another is referred to as typecasting. Modern Pascal compilers support explicit typecasting in the manner of C, with a slightly different syntax. However, typecasting is usually used in low-level situations and in connection with object-oriented programming, and a beginning programming student will not need to use it. Here is information on typecasting from the GNU Pascal manual.
In Pascal, the minus sign can be used to make a value negative. The plus sign can also be used to make a value positive, but is typically left out since values default to positive.
Do not attempt to use two operators side by side, like in: <delphi> some_real := 37.5 * -2; </delphi>
This may make perfect sense to you, since you're trying to multiply by negative-2. However, Pascal will be confused — it won't know whether to multiply or subtract. You can avoid this by using parentheses to clarify: <delphi> some_real := 37.5 * (-2); </delphi>
The computer follows an order of operations similar to the one that you follow when you do arithmetic. Multiplication and division (* / div mod) come before addition and subtraction (+ -), and parentheses always take precedence. So, for example, the value of: 3.5*(2+3) will be 17.5.
Pascal cannot perform standard arithmetic operations on Booleans. There is a special set of Boolean operations. Also, you should not perform arithmetic operations on characters.
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