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Scanf Is the C Library’S Counterpart to Printf Chapter 1: Introducing C Chapter 1: Introducing C Origins of C • By 1971, Ritchie began to develop an extended version of B. Chapter 1 • He called his language NB (“New B”) at first. • As the language began to diverge more from B, he changed its name to C. Introducing C • The language was stable enough by 1973 that UNIX could be rewritten in C. 1 Copyright © 2008 W. W. Norton & Company. 3 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 1: Introducing C Chapter 1: Introducing C Origins of C Standardization of C • C is a by-product of UNIX, developed at Bell • K&R C Laboratories by Ken Thompson, Dennis Ritchie, – Described in Kernighan and Ritchie, The C Programming and others. Language (1978) – De facto standard • Thompson designed a small language named B. • C89/C90 • B was based on BCPL, a systems programming – ANSI standard X3.159-1989 (completed in 1988; formally language developed in the mid-1960s. approved in December 1989) – International standard ISO/IEC 9899:1990 • C99 – International standard ISO/IEC 9899:1999 – Incorporates changes from Amendment 1 (1995) 2 Copyright © 2008 W. W. Norton & Company. 4 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 1: Introducing C Chapter 1: Introducing C C-Based Languages Strengths of C • C++ includes all the features of C, but adds • Efficiency classes and other features to support object- • Portability oriented programming. • Power • Java is based on C++ and therefore inherits many • Flexibility C features. • Standard library • C# is a more recent language derived from C++ and Java. • Integration with UNIX • Perl has adopted many of the features of C. 5 Copyright © 2008 W. W. Norton & Company. 7 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 1: Introducing C Chapter 1: Introducing C Properties of C Weaknesses of C • Low-level • Programs can be error-prone. • Small • Programs can be difficult to understand. • Permissive • Programs can be difficult to modify. 6 Copyright © 2008 W. W. Norton & Company. 8 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 1: Introducing C Chapter 2: C Fundamentals Effective Use of C Program: Printing a Pun • Learn how to avoid pitfalls. #include <stdio.h> • Use software tools (lint, debuggers) to make int main(void) { programs more reliable. printf("To C, or not to C: that is the question.\n"); • Take advantage of existing code libraries. return 0; } • Adopt a sensible set of coding conventions. • This program might be stored in a file named pun.c. • Avoid “tricks” and overly complex code. • The file name doesn’t matter, but the .c extension is • Stick to the standard. often required. 9 Copyright © 2008 W. W. Norton & Company. 2 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 2: C Fundamentals Chapter 2: C Fundamentals Compiling and Linking • Before a program can be executed, three steps are usually necessary: – Preprocessing. The preprocessor obeys commands that Chapter 2 begin with # (known as directives) – Compiling. A compiler translates then translates the C Fundamentals program into machine instructions (object code). – Linking. A linker combines the object code produced by the compiler with any additional code needed to yield a complete executable program. • The preprocessor is usually integrated with the compiler. 1 Copyright © 2008 W. W. Norton & Company. 3 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 2: C Fundamentals Chapter 2: C Fundamentals Compiling and Linking Using cc The GCC Compiler • To compile and link the pun.c program under • GCC is one of the most popular C compilers. UNIX, enter the following command in a terminal • GCC is supplied with Linux but is available for or command-line window: many other platforms as well. % cc pun.c • Using this compiler is similar to using cc: The % character is the UNIX prompt. % gcc -o pun pun.c • Linking is automatic when using cc; no separate link command is necessary. 4 Copyright © 2008 W. W. Norton & Company. 6 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 2: C Fundamentals Chapter 2: C Fundamentals Compiling and Linking Using cc Integrated Development Environments • After compiling and linking the program, cc • An integrated development environment (IDE) is leaves the executable program in a file named a software package that makes it possible to edit, a.out by default. compile, link, execute, and debug a program • The -o option lets us choose the name of the file without leaving the environment. containing the executable program. • The following command causes the executable version of pun.c to be named pun: % cc -o pun pun.c 5 Copyright © 2008 W. W. Norton & Company. 7 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 2: C Fundamentals Chapter 2: C Fundamentals The General Form of a Simple Program Directives • Simple C programs have the form • Before a C program is compiled, it is first edited directives by a preprocessor. • Commands intended for the preprocessor are int main(void) { called directives. statements • Example: } #include <stdio.h> • <stdio.h> is a header containing information about C’s standard I/O library. 8 Copyright © 2008 W. W. Norton & Company. 10 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 2: C Fundamentals Chapter 2: C Fundamentals The General Form of a Simple Program Directives • C uses { and } in much the same way that some • Directives always begin with a # character. other languages use words like begin and end. • By default, directives are one line long; there’s no • Even the simplest C programs rely on three key semicolon or other special marker at the end. language features: – Directives – Functions – Statements 9 Copyright © 2008 W. W. Norton & Company. 11 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 2: C Fundamentals Chapter 2: C Fundamentals Functions Statements • A function is a series of statements that have been • A statement is a command to be executed when grouped together and given a name. the program runs. • Library functions are provided as part of the C • pun.c uses only two kinds of statements. One is implementation. the return statement; the other is the function • A function that computes a value uses a return call. statement to specify what value it “returns”: • Asking a function to perform its assigned task is return x + 1; known as calling the function. • pun.c calls printf to display a string: printf("To C, or not to C: that is the question.\n"); 12 Copyright © 2008 W. W. Norton & Company. 14 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 2: C Fundamentals Chapter 2: C Fundamentals The main Function Statements • The main function is mandatory. • C requires that each statement end with a • main is special: it gets called automatically when semicolon. the program is executed. – There’s one exception: the compound statement. • main returns a status code; the value 0 indicates • Directives are normally one line long, and they normal program termination. don’t end with a semicolon. • If there’s no return statement at the end of the main function, many compilers will produce a warning message. 13 Copyright © 2008 W. W. Norton & Company. 15 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 2: C Fundamentals Chapter 2: C Fundamentals Printing Strings Comments • When the printf function displays a string • A comment begins with /* and end with */. literal—characters enclosed in double quotation /* This is a comment */ marks—it doesn’t show the quotation marks. • Comments may appear almost anywhere in a • printf doesn’t automatically advance to the program, either on separate lines or on the same next output line when it finishes printing. lines as other program text. • To make printf advance one line, include \n • Comments may extend over more than one line. (the new-line character) in the string to be /* Name: pun.c printed. Purpose: Prints a bad pun. Author: K. N. King */ 16 Copyright © 2008 W. W. Norton & Company. 18 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 2: C Fundamentals Chapter 2: C Fundamentals Printing Strings Comments • The statement • Warning: Forgetting to terminate a comment may cause printf("To C, or not to C: that is the question.\n"); the compiler to ignore part of your program: could be replaced by two calls of printf: printf("My "); /* forgot to close this comment... printf("cat "); printf("To C, or not to C: "); printf("has "); /* so it ends here */ printf("that is the question.\n"); printf("fleas"); • The new-line character can appear more than once in a string literal: printf("Brevity is the soul of wit.\n --Shakespeare\n"); 17 Copyright © 2008 W. W. Norton & Company. 19 Copyright © 2008 W. W. Norton & Company. All rights reserved. All rights reserved. Chapter 2: C Fundamentals Chapter 2: C Fundamentals Comments in C99 Types • In C99, comments can also be written in the • Every variable must have a type. following way: • C has a wide variety of types, including int and // This is a comment float. • This style of comment ends automatically at the • A variable of type int (short for integer) can end of a line. store a whole number such as 0, 1, 392, or –2553. • Advantages of // comments: – The largest int value is typically 2,147,483,647 but – Safer: there’s no chance that an unterminated comment can be as small as 32,767. will accidentally consume part of a program.
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