C Programming Revision Malcolm Wilson

Variables Types int, char, double, long. NO type for string see later. unsigned above. assignment X=2 ; C=‘v’;

Keywords C has a small number of “keywords”

Standard I/O printf() scanf() Format specifiers %d, %f, %c, %s

Operations +, -, *, /, %, ^ Operation dependent on variable type Try some

Boolean Any value other than zero is true. Watch out for == “is equal to”.

Control for(i=0, i<9, i++) { code block} while (x<8) {code block} if (y==2) {code block} elseif(y==7) {code block} else {code block}

Control switch( myvar) case 1 : {code block break;} case 2: {code block break;} default {code block} us/library/66k51h7a%28VS.80%29.aspx

Control Code block is surrounded by {} if more than one line. Don’t need {} if code one line long. eg for(i=0; i<5; i++) printf(“ number is: %d /n”, i);

Functions and Prototypes C is composed of functions, and must have at least one function called main(). Functions accept parameters and return values A “prototype” should be written which indicates what data types a function should accept and return. – Eg int mynumberfunction( int num1, int num2) ;

Scope and storage class Used for AVR Static,will remain even after function has exited. Global Volatile, can be changed by unpredicable actions.

Preprocessor directives #include – “localfile” – /usr/include #define – #define WIDTH 80 – #define LENGTH ( WIDTH + 10 ) – #define u8 unsigned char

Arrays and strings int myarray[5]; int myarray[5]={1, 2, 3}; int myarray[]={1,2,3,4,5}; char mychararray=“malcolm”; A string is a “null terminated” char array.

Structures struct struct_name { structure_member;... } instance_1,instance_2 instance_n; OR struct struct_name instance_1,instance_2,instance3 After defining the structure.

Structures Using typedef to avoid struct structurename all the time. typedef struct{ unsigned int house_number; char street_name[50]; int zip_code; char country[50]; } address; address billing_addr; address shipping_addr;

Pointers Declared as using * int *p says p in a pointer to an integer. p points to the memory location where a integer is stored. Confusing, in the code. *p means the contents of memory location p. And &p is the memory address of p.

Pointers and arrays myarray is the same as &myarray[0] So if an array is initialised as char name[]=“malcolm”; *(name+3) will be ‘c’;

Dynamic memory allocation Allocates memory on the “heap” malloc(n) calloc(s, nbytes) intialises memory free();

sizeof() Used for malloc to allocate memory

Pointers and structures #include main() { printf("hello world \n"); struct mystruct{ int age; char buffer[20]; }mydata; mydata.age=45; printf("age is %d \n", mydata.age); struct mystruct * d; d=malloc(sizeof(struct mystruct)); d->age=53; printf("pointed age is %d \n", d->age); }

argv and argc int main (int argc, char *argv[]) { } argc, argument count argv, argument vector

Boo Boo’s in C Forgetting the semicolon Using = in a boolean expression instead of ==. Completing a loop with no code being executed. – while(test); { code block}

Deep C Lvalues, Rvalues Inline functions Pointers to functions Pointers to pointers and multidimensional arrays.