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c 2022, 2023 Richard Stallman and Free Software Foundation, Inc. (The work of Trevis Rothwell and Nelson Beebe has been assigned to the FSF.) Permission is granted to copy, distribute and/or modify this document under
The C Language C is a professional programmer's language. It was designed to get in one's way as little as possible. Kernighan and Ritchie wrote the original language definition in their book, The C Programming Language (below), as part of their research at AT&T. Unix and C++ emerged from the same labs.
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The first is to introduce the C program-ming language. C is a practical and still-current software tool; it remains one of the most popular programming languages in existence, particularly in areas such as embedded systems. C facilitates writing code that is very efficient and powerful and, given the ubiquity of C compilers, can be easily
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- INTRODUCTION: THE C LANGUAGE
- GETTING YOUR FEET WET IN THE C
- 2.1 Hello, somebody
- 2.1.1 An aside on C strings and string-based I/O
- BASIC TYPES AND OPERATORS
- Type combination and promotion
- 3.4.1 Comments
- which may cross multiple lines. C++introduced a form of comment started by two slashes and extending to the end of the line::
- Demotion on assignment
- Meaning
- 3.4.5 Unary Increment Operators: ++ and --
- Meaning
- 3.4.8 Bitwise Operators
- Exercises
- CONTROL STRUCTURES
- 4.1 if Statement
- 4.5 do-while loop
- 4.6.1 break
- 4.6.2 continue
- Memory access eficiency.
- Which header file do I need to include?
- u q
- 6.1 The C struct
- 6.1.3 Arrays of structs and type aliases (typedef)
- The Abstraction Principle
- 7.1 Function syntax
- 7.1.1 main is where it all begins
- 7.1.2 Function naming restrictions and conventions
- 7.2 Data types for parameters and return values
- C-ing and Nothingness --- void
- 7.2.1 Parameters to functions are passed by value
- 7.2.4 Example 3: passing an array to a function
- No function overloading or default parameters in C
- 7.2.5 A longer example
- Static variables and the static storage class
- POINTERS AND MORE ARRAYS
- 8.1 Pointers
- 8.1.1 Declaration syntax
- 8.1.4 Pointers to struct's
- f->numerator = tmp; }
- The const qualifier
- 8.3 Dynamic memory allocation
- 8.3.1 malloc and free
- Pointing into the void
- 8.3.3 Advantages and disadvantages of heap-allocated memory
- Advantages to heap allocation
- Disadvantages to heap allocation
- 8.3.5 C strings revisited
- 8.3.6 Linked lists
- 8.3.7 Pointers to pointers, etc.
- 9.1 The compilation process
- 9.1.1 The preprocessing step
- Header (.h) and source (.c) files
- f->denominator = tmp; }
- Preprocessor directives
- #if
- Multiple #includes
- static functions
- Invoking the preprocessor
- 9.1.2 The compilation step
- 9.1.3 The linking phase
- The main function
- 10.1 Precedence and Associativity
- 10.2 Standard Library Functions
- 10.3 stdio.h
- FILE* fopen(const char* fname, const char* mode);
- 10.5 string.h
is a professional programmer's language. It is a systems implementation language, and was originally designed by Dennis Ritchie at Bell Labs in the 1960s. Prior to the development of C, most operating systems were developed in assembly language1! The C language (and its predecessor, the B language) were designed to provide some level of portability...
In this first chapter, we'll get wet in the C by way of a tutorial that examines a variety of topics that are discussed in depth in later chapters. Where appropriate, pointers to later sections are given if you want to read a bit more as you work through the following examples.
We first start out by examining a simple "hello, world"-style program: a program that simply echoes (prints) what ever is typed on the keyboard, until end-of-file is reached. Here is the code: #include #include int main() { int character; character = getchar(); while (character != EOF) { putchar(character); character = getchar(...
In ordinary C programs, you'll often used string-based I O functions instead of character-based ones. Strings / in C are very much unlike strings in Java or Python: they are simply arrays of characters that are terminated with a "null termination character", which is written \\0 ' '. Notice single quotes are used for literal characters in C and doub...
C provides a standard, though minimal, set of basic data types. Sometimes these are called "primitive" types. This chapter focuses on defining and showing examples of using the various types, including operators and expressions that can be used. More complex data structures can be built up from the basic types described below, as we will see in lat...
The integral types may be mixed together in arithmetic expressions since they are all basically just integers. That includes the char type (unlike Java, in which the byte type would need to be used to specify a single-byte integer). For example, char and int can be combined in arithmetic expressions such as ( b + 5). ' ' How does the compiler deal ...
Comments in C are enclosed by slash/star pairs: /* .. comments .. */
comment until the line end // The // comment form is so handy that many C compilers now also support it, although it is not technically part of the C language. Along with well-chosen function names, comments are an important part of well written code. Comments should not just repeat what the code says. Comments should describe what the code accompl...
The opposite of promotion, demotion moves a value from a type to a smaller type. This is a situation to be avoided, because strictly speaking the result is implementation and compiler-defined. In other words, there's no guarantee what will happen, and it may be diferent depending on the compiler used. A common behavior is for any extra bits to be t...
Addition Subtraction / Division Multiplication % Remainder (mod)
The unary ++ and -- operators increment or decrement the value in a variable. There are "pre" and "post" variants for both operators which do slightly diferent things (explained below). Operator var++ ++var var-- --var
! Boolean not (unary) && Boolean and || Boolean or
C includes operators to manipulate memory at the bit level. This is useful for writing low-level hardware or operating system code where the ordinary abstractions of numbers, characters, pointers, etc... are insufi cient. Using bitwise operators is very common in microcontroller programming environments and in some "systems" software. Bit manipulat...
The theme for the following exercises is dates and times, which often involve lots of interesting calculations (sometimes using truncating integer arithmetic, sometimes using modular arithmetic, sometimes both), and thus good opportunities to use various types of arithmetic operations, comparisons, and assignments. Write a C program that asks for a...
In this chapter, we encounter the set of "control" structures in C, such as conditional statements and looping constructs. As a preview, the control structures in C are nearly identical to those found in Java (since Java syntax is heavily based on C), and bear strong resemblance to control structures found in other programming languages.
Both an if and an if-else are available in C. The can be any valid C expression. The parentheses around the expression are required, even if it is just a single variable: if ( ) // simple form with no {}'s or else clause You should always use curly braces around the statement block associated with an if statement...
Like a while loop, but with the test condition at the bottom of the loop. The loop body will always execute at least once. The do-while tends to be an unpopular area of the language. Although many users of C use the straight while if possible, a do-while loop can be very useful in some situations: do { } while ( );
The break statement causes execution to exit the current loop or switch statement. Stylistically speaking, break has the potential to be a bit vulgar. It is preferable to use a straight while with a single conditional expression at the top if possible, but sometimes you are forced to use a break because the test can occur only somewhere in the mids...
The continue statement causes control to jump to the bottom of the loop, efectively skipping over any code below the continue. As with break, this has a reputation as being vulgar, so use it sparingly. You can almost always get the efect more clearly using an if inside your loop: while ( ) { if ( ) { continue; }
If you know about CPU caches and cache lines, you'll know that it's more eficient to access memory which is near other recently accessed memory. This means that the most eficient way to read through a chunk of the array is to vary the rightmost index the most frequently since that will access elements that are near each other in memory.
For pretty much all C programs you write you will need to #include some header files (headers are discussed in more detail in Program structure and compilation). Which header file will you need? One of the easiest ways to find out is to use the man program in a Linux (or *NIX) shell to read the manual page for a particular C library function. For e...
' ' to go up a page, and ' ' to quit (type h or ' ' ' ? for help on navigating). One confusing aspect of looking up a man page is that the ' same name can appear in multiple sections of the manual pages system. For example, there's a printf C library function, and there is also a printf function available for writing shell scripts. If you just type...
C has a facility for grouping data elements together in the form of a "record", which is called a struct. A struct in C is sort of like a class (in languages with classes), except that (1) all members of the struct are public (i.e., there is no way to "hide" members), and (2) there are no methods, only data members. Members of a struct are often re...
It is perfectly valid, and quite common, to have arrays of records. For example, we might want to have a whole series of fractions stored in an array, as follows:
"Each significant piece of functionality in a program should be implemented in just one place in the source code. Where similar functions are carried out by distinct pieces of code, it is generally beneficial to combine them into one by abstracting out the varying parts." Benjamin C. Pierce, "Types and Programming Languages" (http://www.cis.upenn.e...
A function has a name, a comma-separated list of parameters, the block of code it executes when called, and, optionally, a return value. The basic function definition syntax is: return-type function-name(parameters) { code-block } For example, here is a function that computes and returns n! (n factorial): /* iteratively computes and returns n! if n...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
None of these string routines allocate memory or check that the passed in memory is the right size. The caller is responsible for making sure there is "enough" memory for the operation. The type size_t is an unsigned integer wide enough for the computer's address space (most likely an unsigned long). size_t strlen(const char* string); Return the nu...
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The C Programming Language. C is a high-level language — structured. C is a low-level language — machine access. C is a small language, extendable with libraries. C is permissive: assumes you know what you’re doing. Good: efficient, powerful, portable, flexible. Bad: easy to make errors, obfuscation, little support for modularization.
In 1972 Dennis Ritchie at Bell Labs writes C and in 1978 the publication of The C Programming Language by Kernighan & Ritchie caused a revolution in the computing world. 1.1 Why C? Mainly because it produces code that runs nearly as fast as code written in assembly language, but is a high level programming language. Some examples of the use of C:
