C Programming Training In Ambala ! BATRA COMPUTER CENTRE

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BATRA COMPUTER CENTRE
ISO CERTIFIED 9001:2008

The C Language
 Currently, the most commonly-used language for embedded
systems
 “High-level assembly”
 Very portable: compilers exist for virtually every processor
 Easy-to-understand compilation
 Produces efficient code
 Fairly concise

C History
Developed between 1969 and 1973 along with Unix
Due mostly to Dennis Ritchie
Designed for systems programming
 Operating systems
 Utility programs
 Compilers
 Filters
Evolved from B, which evolved from BCPL

Hello World in C
#include <stdio.h>
Void main ()
{
Printf(“Hello, world !n”);
}
Preprocessor used to
share information
among source files
- Clumsy
+ Cheaply implemented
+ Very flexible

Hello World in C
#include <stdio.h>
Void main ()
{
Printf(“Hello, world !n”);
}
Program mostly a
collection of functions
“main” function special:
the entry point
“void” qualifier
indicates function does
not return anything
I/O performed by a
library function: not
included in the
language

Euclid’s algorithm in C
Int gcd(int m, int n)
{
int r ;
while ( (r = m% n) != 0) {
}
return n ;
}
“New Style” function
declaration lists number
and type of arguments
Originally only listed
return type. Generated
code did not care how
many arguments were
actually passed.
Arguments are call-by-
value

int gcd(int m, int n)
{
int r;
while ( (r = m % n) != 0) {
m = n;
n = r;
}
return n;
}
Automatic variable
Storage allocated on stack
when function entered,
released when it returns.
All parameters, automatic
variables accessed w.r.t.
frame pointer.
Extra storage needed
while evaluating large
expressions also placed on
the stack
n
m
ret. addr.
r
Frame
pointer Stack
pointer
Excess
arguments
simply
ignored

{
int r;
while ( (r = m % n) != 0) {
m = n;
n = r;
}
return n;
}
Expression: C’s basic
type of statement.
Arithmetic and logical
Assignment (=) returns
a value, so can be used
in expressions
% is remainder
!= is not equal

{
int r;
while ( (r = m % n) != 0) {
m = n;
n = r;
}
return n;
} Each function returns a
single value, usually an
integer. Returned
through a specific
register by convention.
High-level control-flow
statement. Ultimately
becomes a conditional
branch.
Supports “structured
programming”

uclid’ Compiled on PDP-1
.globl _gcd r0-r7
.text PC is r7, SP is r6, FP is r5
_gcd:
jsr r5,rsave save sp in frame pointer r5
L2:mov 4(r5),r1 r1 = n
sxt r0 sign extend
div 6(r5),r0 m / n = r0,r1
mov r1,-10(r5) r = m % n
jeq L3
mov 6(r5),4(r5) m = n
mov -10(r5),6(r5) n = r
jbr L2
L3:mov 6(r5),r0 return n in r0
jbr L1
L1:jmp rretrn restore sp ptr, return
{
int r;
while ( (r = m % n) != 0) {
m = n;
n = r;
}
return n;
}

Pieces of C
 Types and Variables
 Definitions of data in memory
 Expressions
 Arithmetic, logical, and assignment operators in an infix notation
 Statements
 Sequences of conditional, iteration, and branching instructions
 Functions
 Groups of statements and variables invoked recursively

C Types
Basic types: char, int, float, and double
Meant to match the processor’s native types
 Natural translation into assembly
 Fundamentally nonportable
Declaration syntax: string of specifiers followed by a
declarator
Declarator’s notation matches that in an expression
Access a symbol using its declarator and get the basic type
back

C StructuresA struct is an object with named fields:
struct {
char *name;
int x, y;
int h, w;
} box;
Accessed using “dot” notation:
box.x = 5;
box.y = 2;

Struct bit-fields Way to aggressively pack data in memory
struct {
unsigned int baud : 5;
unsigned int div2 : 1;
unsigned int use_external_clock : 1;
} flags;
 Compiler will pack these fields into words
 Very implementation dependent: no guarantees of ordering,
packing, etc.
 Usually less efficient
 Reading a field requires masking and shifting

C Unions
 Can store objects of different types at different times
union {
int ival;
float fval;
char *sval;
};
 Useful for arrays of dissimilar objects
 Potentially very dangerous
 Good example of C’s philosophy
*Provide powerful mechanisms that can be abused

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Ph. No.: 9729666670, 8222066670 &0171-4000670
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Website: www.batracomputercentre.com

C Programming Training In Ambala ! BATRA COMPUTER CENTRE

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