That's because C also has the operators '=', '+=' and its kin, '<<', '>>', '++', '--', etc. You can convert In Pascal, a similar end is performed by declaring a subrange of integer (a compiler may then choose to allocate a smaller amount of storage for the declared variable): This subrange feature is not supported by C. A major, if subtle, difference between C and Pascal is how they promote integer operations. Enables the Delphi dialect of Free Pascal. the receiving function gets its own local copy of each argument and Array indices can be any ordinal data type, however, not just ranges: Strings consisting of n (>1) characters are defined as packed arrays with range 1..n. In C expressions, an identifier representing an array is treated as a constant pointer to the first element of the array, thus, given the declarations int a[10] and int *p; the assignment p = a is valid and causes p and a to point to the same array. are performed by zero-checks, false is represented by zero, while true is represented by any other value. the name of the unit. Real types hold floating-point values. Some Pascal dialects also incorporated traits from C. The languages documented here are the Pascal of Niklaus Wirth, as standardized as ISO 7185 in 1982, and the C of Brian Kernighan and Dennis Ritchie, as standardized in 1989. The type ^T means a pointer For example: You can initialize a variable of any record type as you declare it: A variant record is a div and mod can operate only on In its original form (as described by Niklaus Wirth), Pascal qualifies as a managed pointer language, some 30 years before either Java or C#. These operators can compare any values of any ordinal type, and In Pascal, the result of an operation is defined for all integer/subrange types, even if intermediate results do not fit into an integer. For example, schema types support (besides other uses) variable-length arrays while keeping the type-safety of mandatory carrying the array dimension with the array, allowing automatic run-time checks for out-of-range indices also for dynamically sized arrays. You can declare a function pointer type like this: Here is a function whose signature matches this function pointer In Pascal, unlike C, the string's first character element is at index 1 and not 0 (leading it to be length-prefixed). However, a C compiler is never required or expected to handle out of range intermediate results: it is the programmers responsibility to ensure that all intermediate results fit into the operand range. Each distinct record type defines the names and types of the In Pascal a string literal of length n is compatible with the type packed array [1..n] of char. characters you can type on a standard English-language keyboard. Enable tail recursion optimization, which tells the Pascal compiler C uses dedicated operator symbols to a greater extent. on systems using the ASCII character set ord('1') = 49 and chr(9) is a TAB character. are perfectly legal. In C, they are termed "structures". Pascal stems directly from ALGOL W, while it shared some new ideas with ALGOL 68. A Pascal example: The behavior of the types in the two languages however is very different. program will terminate with an error. is a new takes an argument of any pointer type. In most programs you can simply use real for all (The name real is a slight languages.). This is the one place in Pascal where a string values are not limited to 255 characters. I'm getting a bit too far ahead this early in the book, so don't worry if this isn't making much sense right now. In Pascal, we can use the sentence "with name_of_record do" in order to use directly the fields of that record, like local variables, instead of write name_of_record.name_of_field. In C, they are also syntactically part of the statement (transforming an expression into a statement). In C, operands must first be promoted to the size of the required result: intermediate results are undefined if they do not fit into the range of the promoted operands. smallint (2 bytes). Pointer arithmetic (a common source of programming errors in C, especially when combined with endianness issues and platform-independent type sizes) is not permitted in Pascal. However, C is more ALGOL-like than Pascal regarding (simple) declarations, retaining the type-name variable-name syntax. / can operate on integers or reals; it always returns a real. When continue The first version of C appeared in 1972. A static array holds a fixed number of elements. The Pascal compiler has the freedom to use whatever ordering it may prefer and must always evaluate the whole expression even if the result can be determined by partial evaluation. These are useful in if statements: if (x > a value by setting a variable that is passed by reference. And, in fact, they are, as far as the parser is concerned. In C, the underscore counts as a letter, so even _abc is a valid name. This kind of mistake cannot happen in Pascal, as assignments are not expressions and do not have a value: using the wrong operator will cause an unambiguous compilation error, and it's also less likely that anyone would mistake the := symbol for an equality test. When growing a Rather than try to memorize the function of each operator, try instead to learn through careful study of the sample programs and code snippets. The authors of C took a diametrically opposite approach: they treat the operators as different, and in fact, in C there are no fewer than 15 levels. The continue statement continues with the next C string literals are null-terminated; that is to say, a trailing null character as an end-of-string sentinel: Null-termination must be manually maintained for string variables stored in arrays (this is often partly handled by library routines). The forin statement loops over successive values Don't worry about trying to memorize each one. than to: The value of the loop variable is undefined after a for Each pointer is bound to a single dynamic data item, and can only be moved by assignment: Pointers in Pascal are type safe; i.e. If continue is executed during the last iteration of Later, with ANSI C, it obtained constant and type definitions features and the preprocessor also became part of the language, leading to the syntax we see today. The reason is that these versions both represent the mature version of the language, and also because they are comparatively close in time. declared in this section must be implemented in the following This has several In contrast, the corresponding Pascal fragment var Y:^X; is inherently unambiguous; correct parsing does not require a symbol table. may alternatively have any ordinal type, such as integer or boolean. program that uses arrays. When Niklaus Wirth designed Pascal, the desire was to limit the number of levels of precedence (fewer parse routines, after all). The grammars of both languages are of a similar size. declaration introduces a name for a constant: The expression in a constant declaration is evaluated at compile During expression evaluation, and in both languages, a boolean value may be internally stored as a single bit, a single byte, a full machine word, a position in the generated code, or as a condition code in a status register, depending on machine, compiler, and situation; these factors are usually more important than the language compiled. The length() function returns the length of a string. repeat loop. The original Pascal definition appeared in 1969 and a first compiler in 1970. Take a look at this code: if (Started = True) and (X > 20) then Z := X and Y; In this example, the and keyword is being used in two completely different contexts. letters, digits and the underscore character ('_'), and may not begin On every assignment to a variable whose type is a range expression: Certain types are considered to be ordinal types: these This flexibility allows C to manipulate any length array using the same code. Both are descendants of the ALGOL language series. The possible values of boolean are false and true, with ordinal value of false=0 and true=1. concatenate a string with a non-string value, unlike in some other Here there is an example: There is no equivalent feature to with in C. In C, the exact bit length of a field can be specified: How much storage is used depends on traits (e.g., word-alignment) of the target system. as are all declaration sections (uses, type, You can declare a period. Without question, this can be confusing at first. record whose field set can vary depending on the value of a. Short circuit expression evaluation has been commonly considered an advantage for C because of the "evaluation problem": This seemingly straightforward search is problematic in Pascal because the array access a[i] would be invalid for i equal to 11. Thus, dynamic memory allocation is not built into the language processor. To loop through decreasing values, use downto rather similar to var, but does not let the function receive a more efficient, since internally it can be passed by reference. integers, and return an integer. may be any length (unless you forgot to enable Delphi mode, in which function or procedure itself. Declarations may appear in any order. If both operands are Hence, it is not possible to define an array whose length depends in any way on program data. A unit is defined in a Pascal source file that looks like this: The unit declaration at the top of the file specifies with new: The special pointer value nil points to nothing. For example: The dispose function deletes memory that was allocated field values: Code that processes a variant record will often want to use a case For example: You can access a record's fields using the '.' the period at the end. However, a Pascal amalgamated with C would lose that protection by definition. While arrays in C are fixed, pointers to them are interchangeable. In C, the programmer may inspect the byte-level representation of any object by pointing a char pointer to it: It may be possible to do something similar in Pascal using an undiscriminated variant record: Although casting is possible on most Pascal compilers and interpreters, even in the code above a2c.a and a2c.b are not required by any Pascal standardizations to share the same address space. In general, the lower dependence on pointers for basic tasks makes it safer than C in practice. range of values that it may hold: The runtime will check that values are actually in these ranges only It is a common mistake in C, due either to inexperience or to a simple typing error, to accidentally put assignment expressions in conditional statements such as if (a = 10) { }. Pascal does not allow the mixing of arithmetic and Boolean variables, and things like this are caught at the semantic level, when it comes time to generate code for them, rather than at the syntax level. callers variable will be passed by reference, so the caller C and Pascal differ in their interpretation of upper and lower case. non-integer numbers. C (before C99) strictly defines that any declarations must occur before the statements within a particular block but allows blocks to appear within blocks, which is a way to go around this. Also pointers can never be assigned to non-pointer variables. A function or procedure parameter can have an array type with no If you want to store character data in a binary file, you must use consequences, some of which are quite important: integer is longint (4 bytes) rather than If range of the required result is greater than the range of operands, this normally produces slow inefficient code, even from a good optimising compiler. For more information, see the full reference procedures and functions in the implementation section var section before you can use it in a for In C a string generally has the type char[n]. However, since Pascal has nested procedures/functions, jumps can be done from an inner procedure or function to the containing one; this was commonly used to implement error recovery. program. 'the A unit ends with the end keyword followed by a They can start at 0 or field in the record. beginning, the loop body is skipped: no iterations will run. You may define value being assigned is in the range. also strings. Names with a leading underscore are often used to differentiate special system identifiers in C. Both C and Pascal use keywords (words reserved for use by the language). remembered to enable Delphi mode. In both languages, identifiers consist of letters and digits, with the rule that the first character may not be a digit. You can also use + to concatenate two strings. platforms. There is more than one way to avoid this problem. of an array: A while statement loops for as long as a condition is 3) and ((y < 0) or (y > 10)) then +, - and * can operate on integers or reals. In C the character type is char which is a kind of integer that is no longer than short int, . program: Comments using syntaxes (1) and (2) may be nested. Furthermore, operations like a = a + 1; are strictly forbidden in Pascal; instead you would use a:= succ(a);. The body of a repeat statement always executes at least once. statement to branch based on its tag field: A pointer ALGOL introduced programming language support for structured programming, where programs are constructed of single entry and single exit constructs such as if, while, for and case. The biggest difference between C and Pascal is that Pascal supports the explicit use of a "tagfield" for the language processor to determine if the valid component of the variant record is being accessed: In this case, the tagfield q must be set to the right state to access the proper parts of the record. Pascal is strict that declarations must occur before statements, but allows definitions of types and functions not only variable declarations to be encapsulated by function definitions to any level of depth. type: Use the @ (address-of) operator to get a pointer to a named guide at the Free Pascal site. Although in C the arithmetic and Boolean operators are treated separately, the variables are not: a Boolean test can be made on any integer value. variables, and are not visible outside it. terminate with an error. a fixed-size character array, e.g. Note that you must use begin/end to wrap It must be the same as the source file name ANSI C and C99 (the later C standards) features, and features of later implementations of Pascal (Turbo Pascal, Free Pascal) are not included in the comparison, despite the improvements in robustness and functionality that they conferred. For example, Java and C# were created in part to address some of the perceived type security issues of C, and have "managed" pointers that cannot be used to create invalid references. static array like this: The array indices don't need to begin with 1. These types have a much keywords you can use to change Pascals argument-passing behavior. false (for while) or true (for repeat) then In Pascal the number of elements in each array type is determined at compile-time and cannot be changed during the execution of the program. Some operators you will rarely, if ever, use, and others you will use all the time. The program element at the very beginning is optional, The assignment operator := assigns a new value to a variable: The variable itself may appear on the right-hand side: The if statement executes one or more statements if a