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the clanguage

BY

SA

1972 by Ken Thompson and Dennis Ritchie

• developed concurrently with Unix• C++ and Objective-C in 1980’s• ANSI C89, C90, and C99

• GCC (Gnu Compiler Collection)• MSVC (Microsoft Visual C++)

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• imperative/procedural• statically typed• weakly typed

control of memory• explicitly manipulate individual bytes

• “portable assembly”• compact data

• manual allocation

calling convention

• assembly from C• C from assembly

(how functions are called in machine code)

systems programming(operating systems, device drivers)

performance-sensitive code

(games, media players)

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basic data typeschar 1-byte signed integerint n-byte signed integerfloat single-precision floating-pointdouble double-precision floating-point

declarationstype name;

int monkey;float zebra;

functions

returnType name(parameters) {body}

int square(int n){ return n * n;}

int cube(int n){ return square(n) * n;}

char foo(int a, float b, float c){ …}

casting(type) expression

int x = 35;foo((char) x);

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!0 // 1!1 // 0!0.6 // 0!3 // 0!-76.5 // 0

void roger(int x){ if (x == 3) { int z = 9; foo(z); } else { bar(z); // z does not exist } ack(z); // z does not exist}

void roger(int x){ int z = 9; if (x == 3) { foo(z); } else { bar(z); } ack(z);}

int main(){ printf(“Hello, world!”); return 0;}

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value variables

float a = 9.3;

pointers(a data type representing an address)

int *foo;double *bar;char *ack;

reference operator&lvalue

int i;int *p;p = &i;

char c;int *p;p = &c; // error

reference operator&lvalue

int i;int *p;p = &i;

char c;int *p;p = (int *) &c;

dereference operator

*pointer

int i = 3;int *p;p = &i;i = *p + 2;

int i;int *p;p = &i;*p = 6;

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pointer arithmeticint i;int *p;p = &i + 2;i = *p;

can subtract a pointer from a pointercan’t add a pointer to a pointer

char *p;p = (char *) 0xB000FFFF;char c = *p;

int *p;p = 0;if (p) { … } // false

pointer comparisons== !=> <>= <=!

weak typing(can violate data types)

float f;f = 98.6;f = f – 2;char *p;p = (char *)&f + 2;*p = 1;

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memory allocation

• malloc• free

void *p;p = malloc(5);float *f;f = malloc(13);…free(p);free(f);

sizeof operatorsizeof type

sizeof intsizeof doublesizeof(float *)

int *p;p = malloc(7 * sizeof(int));*(p + 6) = 35;…free(p);

int *p;p = malloc(7 * (sizeof int));if (p == 0) {

… // allocation failed} else {

… // allocation succeeded

free(p);}

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array(a stack-allocated contiguous block of memory)

type name[size];

float jack[8];char jill[200];

int i[32];char c[11];int *p;p = i;*i = -6;*(i + 1) = 8;*(c + 7) = (char) 5;

int sum(int *arr, int n){

int i = 0;int sum = 0;while (i < n) {

sum = *(arr + i) + sum;i = i + 1;

}return sum;

}

int a[30];…int sumA = sum(a, 30);

int *b = malloc(20 * sizeof(int));…int sumB = sum(b, 20);

char *fred(){

char c[30];return c;

}

char *fred(){

char *c = malloc(30 * sizeof(char));

return c;}

char *foo = fred();…free(foo);

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stringschar *s = “abc”;char b = *(s + 1);int i = strlen(s);

structure(a programmer-defined compound data type)

struct typeName {members};

struct typeName name;instance.member

struct cat {char *name;int age;

}; // semi-colon!

struct cat mittens;mittens.name = “Mittens”;mittens.age = 5;

struct cat mittens;struct cat fluffy;…mittens = fluffy;

struct cat *p = &fluffy;

mittens == fluffy // illegal

struct cat cats[8];

(*cats).name = “Oscar”;(*(cats + 1)).name = “Kitty”;

struct cat *cats = malloc(8 * (sizeof struct

cat));

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