1 COMP 2130 Introduction to Computer Systems Computing Science Thompson Rivers University

1. Introduction 2 The C programming language was designed by Dennis Ritchie at Bell Laboratories in the early 1970s Influenced by ALGOL 60 (1960), CPL (Cambridge, 1963), BCPL (Martin Richard, 1967), B (Ken Thompson, 1970) Traditionally used for systems programming, though this may be changing in favor of C++ Traditional C: The C Programming Language, by Brian Kernighan and Dennis Ritchie, 2 nd Edition, Prentice Hall Referred to as K&R

Standard C  Standardized in 1989 by ANSI (American National Standards Institute) known as ANSI C  International standard (ISO) in 1990 which was adopted by ANSI and is known as C89  As part of the normal evolution process the standard was updated in 1995 (C95) and 1999 (C99)  C++ and C ◦ C++ extends C to include support for Object Oriented Programming and other features that facilitate large software development projects ◦ C is not strictly a subset of C++, but it is possible to write “Clean C” that conforms to both the C++ and C standards.

Elements of a C Program 4  A C development environment includes ◦ System libraries and headers: a set of standard libraries and their header files. For example see /usr/include and glibc. ◦ Application Source: application source and header files ◦ Compiler: converts source to object code for a specific platform ◦ Linker: resolves external references and produces the executable module  User program structure ◦ there must be one main function where execution begins when the program is run. This function is called main  int main (void) {... },  int main (int argc, char *argv[]) {... }  UNIX Systems have a 3 rd way to define main(), though it is not POSIX.1 compliant int main (int argc, char *argv[], char *envp[]) ◦ additional local and external functions and variables

A Simple C Program 5  Create example file: try.c  Compile using gcc: gcc –o try try.c  The standard C library libc is included automatically  Execute program./try  Note, I always specify an absolute path  Normal termination: void exit(int status); ◦ calls functions registered with at exit() ◦ flush output streams ◦ close all open streams ◦ return status value and control to host environment /* you generally want to * include stdio.h and * stdlib.h * */ #include int main (void) { printf(“Hello World\n”); exit(0); }

Getting Started 6  C program files should end with “.c”. ◦ hello.c #include // similar to import statements in Java // stdio.h includes the information about the standard library int main()// similar to main method in Java { printf (“hello, world\n”); // printf() defined in stdio.h return 0; }  How to compile? ◦ $ gcc hello.cor ◦ $ gcc hello.c -o hello ◦ If you do not have anything wrong, you will see a.out in the same working directory.  How to run? ◦ $./a.out

Source and Header files 7  Just as in Java, place related code within the same module (i.e. file).  Header files (*.h) export interface definitions ◦ function prototypes, data types, macros, inline functions and other common declarations  Do not place source code (i.e. definitions) in the header file with a few exceptions. ◦ inline’d code ◦ class definitions ◦ const definitions  C preprocessor (cpp) is used to insert common definitions into source files  There are other cool things you can do with the preprocessor

Another Example C Program 8 example.c /* this is a C-style comment * You generally want to palce * all file includes at start of file * */ #include int main (int argc, char **argv) { // this is a C++-style comment // printf prototype in stdio.h printf(“Hello, Prog name = %s\n”, argv[0]); exit(0); } /* comments */ #ifndef _STDIO_H #define _STDIO_H... definitions and protoypes #endif /usr/include/stdio.h /* prevents including file * contents multiple * times */ #ifndef _STDLIB_H #define _STDLIB_H... definitions and protoypes #endif /usr/include/stdlib.h #include directs the preprocessor to “include” the contents of the file at this point in the source file. #define directs preprocessor to define macros.

C Standard Header Files 9  Standard Headers you should know about: ◦ stdio.h – file and console (also a file) IO: perror, printf, open, close, read, write, scanf, etc. ◦ stdlib.h - common utility functions: malloc, calloc, strtol, atoi, etc ◦ string.h - string and byte manipulation: strlen, strcpy, strcat, memcpy, memset, etc. ◦ ctype.h – character types: isalnum, isprint, isupper, tolower, etc. ◦ errno.h – defines errno used for reporting system errors ◦ math.h – math functions: ceil, exp, floor, sqrt, etc. ◦ signal.h – signal handling facility: raise, signal, etc ◦ stdint.h – standard integer: intN_t, uintN_t, etc ◦ time.h – time related facility: asctime, clock, time_t, etc.

C Library Functions: Examples 10

The Preprocessor 11  The C preprocessor permits you to define simple macros that are evaluated and expanded prior to compilation.  Commands begin with a ‘#’. Abbreviated list: ◦ #define : defines a macro ◦ #undef : removes a macro definition ◦ #include : insert text from file ◦ #if : conditional based on value of expression ◦ #ifdef : conditional based on whether macro defined ◦ #ifndef : conditional based on whether macro is not defined ◦ #else : alternative ◦ #elif : conditional alternative ◦ defined() : preprocessor function: 1 if name defined, else 0 #if defined(__NetBSD__)

Common features 12 ◦ For the statement printf (“hello, world\n”); ◦ “…” is a character string. This is also called a string constant.  printf() is a library function to print a string to the terminal.  The C library function int scanf(const char *format,...) reads formatted input from stdin. Data types -  primitive data types char, int, (short & long), float, double

Format specifiers 13 Summary of printf() format specifiers %dprint as decimal integer %6dprint as decimal integer, at least 6 characters wide %fprint as floating point %6fprint as floating point, at least 6 characters wide %.2fprint as floating point, 2 characters after decimal point %6.2fprint as floating point, at least 6 characters wide and 2 after decimal point Other format specifiers %ofor octal %xfor hexadecimal %cfor character %sfor character string %% itself

Example 14 ◦ The following example shows the usage of scanf() function. #include int main() { char str1[20], str2[30]; printf("Enter name: "); scanf("%s", &str1); printf("Enter your website name: "); scanf("%s", &str2); printf("Entered Name: %s\n", str1); printf("Entered Website:%s\n", str2); return(0); }

Operators 15  Mathematical –Subtraction, also unary minus +Addition *Multiplication /Division %Modulus --Decrement ++Increment  Relational >Greater than >=Greater than or equal <Less than <=Less than or equal = =Equal !=Not equal

Operators 16  Logical Operators: &&AND ||OR !NOT

Control structures 17 Control structures  if,  if-else,  for,  while,  do-while,  switch

Exercise 18  write a program to convert Fahrenheit temperature to Celsius temperature, using the given formula formula: ◦ Ask user for an option for  C -> F Or  F -> C

Precedence and Associativity 19

20 Examples x =10;y = ++x; y 11 x =10;y = x++; y 10 int i = 3, j = 2, k; i++;i j = ++i;ji k = i++;k i k = (--j+3)kj

21 l = 4; n = 3; m = 2; x = l * n + m++; After the assignment to x. m 14 3

22 int a,b; a = 1; b = 12; printf (“a+++b = %d\n”, a+++b); a = 1; b = 12; printf (“a++ +b = %d\n”, a++ +b); a = 1; b = 12; printf (“a+ ++b =% d\n”, a+ ++b);

Precedence and Associativity 23

24 Both are lower in precedence than the arithmetic operators. 10 > > (1 + 12) FALSE 0 Associativity: left to right. int x; x = 100; printf(''%d", (x>10)); __?

Logical Operators in C: Example 25 #include main() { int a = 5; int b = 20; int c ; if ( a && b ) { printf("Line 1 - Condition is true\n" ); } if ( a || b ) { printf("Line 2 - Condition is true\n" ); } /* lets change the value of a and b */ a = 0; b = 10; if ( a && b ) { printf("Line 3 - Condition is true\n" ); } else { printf("Line 3 - Condition is not true\n" ); } if ( !(a && b) ) { printf("Line 4 - Condition is true\n" ); } }

Example 26 See

Answer 27

Comma operator 28  Lowest precedence of all the operators.  Causes a sequence of operations, “do this and this and this…”.  Is a binary operator. expression_1, expression_2  Associates left to right. expression_1 is evaluated first expression_2 is evaluated second

Comma operator – Ex. 29  The Comma Expression as a whole has the value and type of expression_2.

Conditional Operator (Ternary) 30 A powerful and convenient operator that replaces certain statements of the if-then-else form. Exp1 ? Exp2: Exp3

Example 31 It is also possible to nest ternary

Expressions Vs Statements 32 An expression in C is any valid combination of operators, constants, functions and variables. A statement is a valid expression followed by a semicolon. Func1(); A function call as a statement. Y = X + Y; An assignment statement.

Symbolic Constants TRU-COMP2130 C Programming 33 #define name replacement_list #include #define LOWER 0// similar to final variable in Java #define UPPER 300 #define STEP 20 main() { float fahr, celsius; for (fahr = LOWER; fahr <= UPPER; fahr = fahr + STEP) { celsius = 5 * (fahr-32) / 9; printf("%3.0f\t%6.1f\n", fahr, celsius); }

Character Input and Output 34 #include /* copy input to output; 1st version */ main() { int c; c = getchar();// in order to read a character while (c != EOF) {// EOF is defined in stdio.h. // EOF means End of File, ^D. putchar(c);// in order to print a character c = getchar(); } }

35 #include /* copy input to output; 2nd version */ main() { int c; while ((c = getchar()) != EOF)// okay? putchar(c); } What if we use the follow code instead? while (c = getchar() != EOF) The above code is equivalent to while (c = (getchar() != EOF)) This is because the precedence of != is higher than =

Think Idea 36 c = (c > =‘a’ && c < = ‘z’) ? c - (‘z’ - ‘Z’):c;