C tutorial
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The document outlines fundamental concepts of the C programming language, including data types, variable declarations, operations, control structures, and functions. It provides detailed examples, explanations of pointers, memory allocation techniques, and command-line argument handling, ultimately aiming to equip the reader with basic programming skills in C. Additionally, it highlights important programming practices, such as the distinction between declaration and definition, and dynamic memory management.
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An example
int global = 10; //global variable
int func (int x)
{
static int stat_var; //static local variable
int temp; //(normal) local variable
int name[50]; //(normal) local variable
……
}](https://image.slidesharecdn.com/ctutorial-151015081011-lva1-app6891/85/C-tutorial-11-320.jpg)
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Arrays
int ids[50];
char name[100];
int table_of_num[30][40];
Accessing an array
ids[0] = 40;
i = ids[1] + j;
table_of_num[3][4] = 100;
Note: In C Array subscripts start at 0 and end one
less than the array size. [0 .. n-1]
Arrays & Strings](https://image.slidesharecdn.com/ctutorial-151015081011-lva1-app6891/85/C-tutorial-36-320.jpg)
![
Strings
Strings are defined as arrays of characters.
The only difference from a character array is, a
symbol “0” is used to indicate the end of a string.
For example, suppose we have a character array, char
name[8], and we store into it a string “Dave”.
Note: the length of this string 4, but it occupies 5
bytes.
DD aa vv ee 00](https://image.slidesharecdn.com/ctutorial-151015081011-lva1-app6891/85/C-tutorial-37-320.jpg)
![
Pointers and Arrays
Pointers and arrays are very closely linked in C.
Array elements arranged in consecutive memory
locations
Accessing array elements using pointers
int ids[50];
int * p = &ids[0];
p[i] <=> ids[i]
Pointers and Strings
A string can be represented by a char * pointer.](https://image.slidesharecdn.com/ctutorial-151015081011-lva1-app6891/85/C-tutorial-46-320.jpg)
![
Char name[50];
name[0] = ‘D’;
name[1] = ‘a’;
name[2] = ‘v’;
name[3] = ‘e’;
name[4] = ‘0’;
char * p = &name[0];
printf(“The name is %s n”, p);
Note: The p represents the string “Dave”, but not the
array
name[50].](https://image.slidesharecdn.com/ctutorial-151015081011-lva1-app6891/85/C-tutorial-47-320.jpg)
![
In C you can pass arguments to main() function.
main() prototype
int main(int argc, char * argv[]);
argc indicates the number of arguments
argv is an array of input string pointers.
How to pass your own arguments?
./hello 10
Command-Line Argument](https://image.slidesharecdn.com/ctutorial-151015081011-lva1-app6891/85/C-tutorial-48-320.jpg)
![
What value is argc and argv?
Let’s add two printf statement to get the value of argc
and argv.
#include <stdio.h>
int main(int argc, char * argv[]);)
{
int i=0;
printf("Hello Worldn");
printf(“The argc is %d n”, argc);
for(i=0; i < argc; i++){
printf(“The %dth element in argv is %sn”, i, argv[i]);
}
return(0);
}](https://image.slidesharecdn.com/ctutorial-151015081011-lva1-app6891/85/C-tutorial-49-320.jpg)
![
The output
The argc is 2
The 0th element in argv is ./hello
The 1th element in argv is 10
The trick is the system always passes the name of the
executable file as the first argument to the main() function.
How to use your argument?
Be careful. Your arguments to main() are always in string format.
Taking the above program for example, the argv[1] is string “10”,
not a number. You must convert it into a number before you can
use it.](https://image.slidesharecdn.com/ctutorial-151015081011-lva1-app6891/85/C-tutorial-50-320.jpg)
![
A data structure is a collection of one or more variables, possibly
of different types.
An example of student record
struct stud_record{
char name[50];
int id;
int age;
int major;
……
};
Data Structure](https://image.slidesharecdn.com/ctutorial-151015081011-lva1-app6891/85/C-tutorial-51-320.jpg)
![ Replacing numbers in your code with macros
- don’t use magic numbers directly
#define MAX_NAME_LEN 50;
char name[MAX_NAME_LEN];
Avoiding global variables
- modulation is more important
Giving variables and functions a nice name
- a meaning name
Don’t repeat your code
- make a subroutine/function
Don’t let the function body to exceed one screen
- hard to debug
Programming Tips](https://image.slidesharecdn.com/ctutorial-151015081011-lva1-app6891/85/C-tutorial-58-320.jpg)
C tutorial
- 1. CSU480CSU480
- 2. “Hello World" Program Data Types & Variables printf() Arithmetic & Logical Operations Conditionals Loops Arrays & Strings Outline PointersPointers FunctionsFunctions Command-Line ArgumentCommand-Line Argument Data StructureData Structure Memory AllocationMemory Allocation Programming TipsProgramming Tips CC vvs. C++s. C++ Books recommendedBooks recommended
- 3. The source code #include <stdio.h> int main() { printf("Hello Worldn"); return(0); } Hello World Program
- 4. Hello World Program How to compile? $ gcc hello.c –o hello gccgcc compiling commandcompiling command hello.chello.c source filesource file hellohello compiler-generated executable filecompiler-generated executable file Note: the default output filename is “Note: the default output filename is “a.outa.out””
- 5. How to execute? ./hello “./ ” indicates the following file “hello” resides under the current directory. Hello World Program Q: why “.” is not included in $PATHQ: why “.” is not included in $PATH environment variable?environment variable?
- 6. Hello World Program A: security consideration. CommandCommand LocationLocation CommentComment lsls /bin/ls/bin/ls provided by theprovided by the systemsystem lsls current directorycurrent directory virusvirus
- 7. NameName DescriptionDescription Size*Size* Range*Range* charchar Character or smallCharacter or small integerinteger 1 byte1 byte signed: -128 to 127signed: -128 to 127 unsigned: 0 to 255unsigned: 0 to 255 short intshort int (short)(short) Short integerShort integer 2 bytes2 bytes signed: -32768 to 32767signed: -32768 to 32767 unsigned: 0 to 65535unsigned: 0 to 65535 intint IntegerInteger 4 bytes4 bytes signed: -2147483648 tosigned: -2147483648 to 21474836472147483647 unsigned: 0 to 4294967295unsigned: 0 to 4294967295 long intlong int (long)(long) Long integerLong integer 4 bytes4 bytes signed: -2147483648 tosigned: -2147483648 to 21474836472147483647 unsigned: 0 to 4294967295unsigned: 0 to 4294967295 floatfloat Floating pointFloating point numbernumber 4 bytes4 bytes 3.4e +/- 38 (7 digits)3.4e +/- 38 (7 digits) doubledouble Double precisionDouble precision floating point numberfloating point number 8 bytes8 bytes 1.7e +/- 308 (15 digits)1.7e +/- 308 (15 digits) longlong doubledouble Long doubleLong double precision floatingprecision floating point numberpoint number 8 bytes8 bytes 1.7e +/- 308 (15 digits)1.7e +/- 308 (15 digits) Data types
- 8. Variable Declaration int length = 100; char num = ‘9’; //The actual value is 57 float deposit = 240.5; unsigned short ID = 0x5544; Try the following statements, and see what happens unsigned char value = -1; printf(“The value is %d n”, value); unsigned char value = 300; printf(“The value is %d n”, value);
- 9. Result DefinitionDefinition Memory layoutMemory layout DisplayDisplay commentcomment unsigned charunsigned char value = -1value = -1 1111111111111111 255255 unsigned charunsigned char value = 300value = 300 0010110000101100 4444 overflowoverflow
- 10. Local variable Local variables are declared within the body of a function, and can only be used within that function. Static variable Another class of local variable is the static type. It is specified by the keyword static in the variable declaration. The most striking difference from a non-static local variable is, a static variable is not destroyed on exit from the function. Global variable A global variable declaration looks normal, but is located outside any of the program's functions. So it is accessible to all functions. Variable types
- 11. An example int global = 10; //global variable int func (int x) { static int stat_var; //static local variable int temp; //(normal) local variable int name[50]; //(normal) local variable …… }
- 12. Variable Definition vs Declaration DefinitionDefinition Tell the compiler about the variable: its typeTell the compiler about the variable: its type and name, as well as allocated a memory cell forand name, as well as allocated a memory cell for the variablethe variable DeclarationDeclaration DDescribe information ``about'' the variableescribe information ``about'' the variable,, doesn’tdoesn’t allocate memory cell for the variableallocate memory cell for the variable
- 14. The printf() function can be instructed to print integers, floats and string properly. The general syntax is printf( “format”, variables); An example int stud_id = 5200; char * name = “Mike”; printf(“%s ‘s ID is %d n”, name, stud_id); printf()
- 15. Format Identifiers %d decimal integers %x hex integer %c character %f float and double number %s string %p pointer How to specify display space for a variable? printf(“The student id is %5d n”, stud_id); The value of stud_id will occupy 5 characters space in the print-out.
- 16. Why “n” It introduces a new line on the terminal screen. aa alert (bell) characteralert (bell) character backslashbackslash bb backspacebackspace ?? question markquestion mark ff formfeedformfeed ’’ single quotesingle quote nn newlinenewline ”” double quotedouble quote rr carriage returncarriage return 000000 octal numberoctal number tt horizontal tabhorizontal tab xhhxhh hexadecimal numberhexadecimal number vv vertical tabvertical tab escape sequence
- 19. Increment and Decrement Operators awkwardawkward easyeasy easiesteasiest x = x+1;x = x+1; x += 1x += 1 x++x++ x = x-1;x = x-1; x -= 1x -= 1 x--x--
- 20. Arithmetic operators int i = 10; int j = 15; int add = i + j; //25 int diff = j – i; //5 int product = i * j; // 150 int quotient = j / i; // 1 int residual = j % i; // 5 i++; //Increase by 1 i--; //Decrease by 1 Example
- 21. Comparing them int i = 10; int j = 15; float k = 15.0; j / i = ? j % i = ? k / i = ? k % i = ?
- 22. The Answer j / i = 1; j % i = 5; k / i = 1.5; k % i It is illegal. Note: For %, the operands can only be integers.
- 23. What is “true” and “false” in C In C, there is no specific data type to represent “true” and “false”. C uses value “0” to represent “false”, and uses non- zero value to stand for “true”. Logical Operators A && B => A and B A || B => A or B A == B => Is A equal to B? A != B => Is A not equal to B? Logical Operations
- 24. A > B => Is A greater than B? A >= B => Is A greater than or equal to B? A < B => Is A less than B? A <= B => Is A less than or equal to B? Don’t be confused && and || have different meanings from & and |. & and | are bitwise operators.
- 25. Short circuiting means that we don't evaluate the second part of an AND or OR unless we really need to. Some practices Please compute the value of the following logical expressions? Short circuiting
- 26. int i = 10; int j = 15; int k = 15; int m = 0; if( i < j && j < k) => if( i != j || k < j) => if( j<= k || i > k) => if( j == k && m) => if(i) => if(m || j && i ) =>
- 27. int i = 10; int j = 15; int k = 15; int m = 0; if( i < j && j < k) => false if( i != j || k < j) => true if( j<= k || i > k) => true if( j == k && m) => false if(i) => true if(m || j && i ) => true Did you get the correct answers?
- 28. if statement Three basic formats, if (expression){ statement … } if (expression) { statement … }else{ statement … } Conditionals
- 29. if (expression) { statement… }else if (expression) { statement… }else{ statement… }
- 30. An example if(score >= 90){ a_cnt ++; }else if(score >= 80){ b_cnt++; }else if(score >= 70){ c_cnt++; }else if (score>= 60){ d_cnt++ }else{ f_cnt++ }
- 31. The switch statement switch (expression) { case item1: statement; break; case item2: statement; break; default: statement; break; }
- 32. for statement for (expression1; expression2; expression3){ statement… } expression1 initializes; expression2 is the terminate test; expression3 is the modifier; Loops
- 33. An example int x; for (x=0; x<3; x++) { printf("x=%dn",x); } First time: x = 0; Second time: x = 1; Third time: x = 2; Fourth time: x = 3; (don’t execute the body)
- 34. The while statement while (expression) { statement … } while loop exits only when the expression is false. An example int x = 3; while (x>0) { printf("x=%d n",x); x--; }
- 35. for (expression1; expression2; expression3){ statement… } for <==> while expression1;expression1; while (expression2)while (expression2) {{ statementstatement……;; expression3;expression3; }} equals
- 36. Arrays int ids[50]; char name[100]; int table_of_num[30][40]; Accessing an array ids[0] = 40; i = ids[1] + j; table_of_num[3][4] = 100; Note: In C Array subscripts start at 0 and end one less than the array size. [0 .. n-1] Arrays & Strings
- 37. Strings Strings are defined as arrays of characters. The only difference from a character array is, a symbol “0” is used to indicate the end of a string. For example, suppose we have a character array, char name[8], and we store into it a string “Dave”. Note: the length of this string 4, but it occupies 5 bytes. DD aa vv ee 00
- 38. Functions are easy to use; they allow complicated programs to be broken into small blocks, each of which is easier to write, read, and maintain. This is called modulation. How does a function look like? returntype function_name(parameters…) { local variables declaration; function code; return result; } Functions
- 39. Sample function int addition(int x, int y) { int add; add = x + y; return add; } How to call a function? int result; int i = 5, j = 6; result = addition(i, j);
- 40. Pointer is the most beautiful (ugliest) part of C, but also brings most trouble to C programmers. Over 90% bugs in the C programs come from pointers. “The International Obfuscated C Code Contest ” (http://www.ioccc.org/) What is a pointer? A pointer is a variable which contains the address in memory of another variable. In C we have a specific type for pointers. Pointers
- 41. Declaring a pointer variable int * pointer; char * name; How to obtain the address of a variable? int x = 0x2233; pointer = &x; where & is called address of operator. How to get the value of the variable indicated by the pointer? int y = *pointer;
- 42. 3333 2222 0000 0000 0x5200 0x5203 0x5200 pointer What happens in the memory? Suppose the address of variable x is 0x5200 in the above example, so the value of the variable pointer is 0x5200. X
- 43. swap the value of two variables
- 44. Why is the left one not working? swap main x, y a, b call swap(a, b) in main x, y, a, b are all local variables
- 45. Why is the right one working?
- 46. Pointers and Arrays Pointers and arrays are very closely linked in C. Array elements arranged in consecutive memory locations Accessing array elements using pointers int ids[50]; int * p = &ids[0]; p[i] <=> ids[i] Pointers and Strings A string can be represented by a char * pointer.
- 47. Char name[50]; name[0] = ‘D’; name[1] = ‘a’; name[2] = ‘v’; name[3] = ‘e’; name[4] = ‘0’; char * p = &name[0]; printf(“The name is %s n”, p); Note: The p represents the string “Dave”, but not the array name[50].
- 48. In C you can pass arguments to main() function. main() prototype int main(int argc, char * argv[]); argc indicates the number of arguments argv is an array of input string pointers. How to pass your own arguments? ./hello 10 Command-Line Argument
- 49. What value is argc and argv? Let’s add two printf statement to get the value of argc and argv. #include <stdio.h> int main(int argc, char * argv[]);) { int i=0; printf("Hello Worldn"); printf(“The argc is %d n”, argc); for(i=0; i < argc; i++){ printf(“The %dth element in argv is %sn”, i, argv[i]); } return(0); }
- 50. The output The argc is 2 The 0th element in argv is ./hello The 1th element in argv is 10 The trick is the system always passes the name of the executable file as the first argument to the main() function. How to use your argument? Be careful. Your arguments to main() are always in string format. Taking the above program for example, the argv[1] is string “10”, not a number. You must convert it into a number before you can use it.
- 51. A data structure is a collection of one or more variables, possibly of different types. An example of student record struct stud_record{ char name[50]; int id; int age; int major; …… }; Data Structure
- 52. A data structure is also a data type struct stud_record my_record; struct stud_record * pointer; pointer = & my_record; Accessing a field inside a data structure my_record.id = 10; “.” or pointer->id = 10; “->”
- 53. Stack memory allocation Non-static local variable is an example of stack memory allocation. Such memory allocations are placed in a system memory area called the stack. Static memory allocation Static local variable and global variable require static memory allocation. Static memory allocation happens before the program starts, and persists through the entire life time of the program. Memory Allocation
- 54. Dynamic memory allocation It allows the program determine how much memory it needs at run time, and allocate exactly the right amount of storage. The region of memory where dynamic allocation and deallocation of memory can take place is called the heap. Note: the program has the responsibility to free the dynamic memory it allocated.
- 56. Functions for the dynamic memory allocation void *malloc(size_t number_of_bytes); allocates dynamic memory size_t sizeof(type); returns the number of bytes of type void free(void * p) releases dynamic memory allocation An example of dynamic memory allocation int * ids; //id arrays int num_of_ids = 40; ids = malloc( sizeof(int) * num_of_ids); …….. Processing …... free(ids);
- 57. Allocating a data structure instance struct stud_record * pointer; pointer = malloc(sizeof(struct stud_record)); pointer->id = 10; Never calculate the size of data structure yourself. The reason is the size of data types is machine- dependent. Give it to sizeof() function. size of intsize of int 32-bytes machines32-bytes machines 3232 64-bytes machines64-bytes machines 6464
- 58. Replacing numbers in your code with macros - don’t use magic numbers directly #define MAX_NAME_LEN 50; char name[MAX_NAME_LEN]; Avoiding global variables - modulation is more important Giving variables and functions a nice name - a meaning name Don’t repeat your code - make a subroutine/function Don’t let the function body to exceed one screen - hard to debug Programming Tips
- 59. Indenting your code (clearance) if(expression) { if(expression) { …… } } Commenting your code Don’t rush into coding. Plan first. Printing out more debugging information Using debugger (gdb)
- 60. C++ is a superset of C C++ has all the characteristics of C Using g++ to compile your source code C vs. C++
- 61. Thanks