Difference between revisions of "Basic Pascal Tutorial/Chapter 1/Assignment and Operations"
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+ | {{Basic Pascal Tutorial/Chapter 1/Assignment and Operations}} | ||
+ | {{TYNavigator|Chapter 1/Variables and Data Types|Chapter 1/Standard Functions}} | ||
+ | |||
1E - Assignment and Operations (author: Tao Yue, state: unchanged) | 1E - Assignment and Operations (author: Tao Yue, state: unchanged) | ||
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To assign a value to a variable, follow this syntax: | To assign a value to a variable, follow this syntax: | ||
− | <syntaxhighlight> | + | |
+ | <syntaxhighlight lang="pascal"> | ||
variable_name := expression; | variable_name := expression; | ||
</syntaxhighlight> | </syntaxhighlight> | ||
+ | |||
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: | ||
− | <syntaxhighlight> | + | |
+ | <syntaxhighlight lang="pascal"> | ||
some_real := 385.385837; | some_real := 385.385837; | ||
</syntaxhighlight> | </syntaxhighlight> | ||
+ | |||
or it can be an arithmetic sequence: | or it can be an arithmetic sequence: | ||
− | <syntaxhighlight> | + | |
+ | <syntaxhighlight lang="pascal"> | ||
some_real := 37573.5 * 37593 + 385.8 / 367.1; | some_real := 37573.5 * 37593 + 385.8 / 367.1; | ||
</syntaxhighlight> | </syntaxhighlight> | ||
+ | |||
The arithmetic operators in Pascal are: | The arithmetic operators in Pascal are: | ||
+ | |||
{| style="background-color:#f5f5f5" cellspacing=5 | {| style="background-color:#f5f5f5" cellspacing=5 | ||
!Operator !!Operation !!Operands !!Result | !Operator !!Operation !!Operands !!Result | ||
Line 36: | Line 46: | ||
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: | ||
− | <syntaxhighlight> | + | |
+ | <syntaxhighlight lang="pascal"> | ||
var | var | ||
some_int : integer; | some_int : integer; | ||
some_real : real; | some_real : real; | ||
</syntaxhighlight> | </syntaxhighlight> | ||
− | When the following block of statements executes | + | |
− | <syntaxhighlight> | + | When the following block of statements executes: |
+ | |||
+ | <syntaxhighlight lang="pascal"> | ||
some_int := 375; | some_int := 375; | ||
some_real := some_int; | some_real := some_int; | ||
</syntaxhighlight> | </syntaxhighlight> | ||
+ | |||
<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>. | ||
− | 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. | + | 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 [http://www.gnu-pascal.de/gpc-es/Type-Casts.html 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. | 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: | Do not attempt to use two operators side by side, like in: | ||
− | <syntaxhighlight> | + | |
+ | <syntaxhighlight lang="pascal"> | ||
some_real := 37.5 * -2; | some_real := 37.5 * -2; | ||
</syntaxhighlight> | </syntaxhighlight> | ||
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: | ||
− | <syntaxhighlight> | + | |
+ | <syntaxhighlight lang="pascal"> | ||
some_real := 37.5 * (-2); | some_real := 37.5 * (-2); | ||
</syntaxhighlight> | </syntaxhighlight> | ||
Line 66: | Line 82: | ||
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. | 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. | ||
− | {| | + | {{TYNavigator|Chapter 1/Variables and Data Types|Chapter 1/Standard Functions}} |
− | |||
− | |||
− | |||
− | |} | ||
− | |||
− |
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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:
variable_name := expression;
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:
some_real := 385.385837;
or it can be an arithmetic sequence:
some_real := 37573.5 * 37593 + 385.8 / 367.1;
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:
var
some_int : integer;
some_real : real;
When the following block of statements executes:
some_int := 375;
some_real := some_int;
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:
some_real := 37.5 * -2;
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:
some_real := 37.5 * (-2);
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.