Embed Size (px)
Citation preview
Introduction to Computer Algorithmics and Programming
Ceng 113
Variables and Operators in C
C Language
C was developed at Bell Laboratories.
(Brian Kernighan and Dennis Richie)-1972
C is known as a high low-level language.
Reference Book
In Library:
C The Complete Reference, Covers C++ & ANSI C
Author; Herbert Schildt
Press; Osborne, McGraw-Hill
ISBN 0-07-881538-X
E-book:
The C Programming Language (ANSI C)
Authors: Brian W. Kernighan,
Dennis M. Ritchie
Program Definitions
• Variable: a named location in memory for storing data.
• Constant: a variable whose value is determined when a
program description is written and doesn’t change from
that value during program execution.
• Label: a named location in memory for storing a
program instruction.
General Form of a C Program
global declarationsreturn-type main(parameter list){
statement sequence}return-type f1(parameter list){
statement sequence}return-type f2(parameter list){
statement sequence}....
• Consist of one or more
functions.
• “main(..)”, which is the first
function called, when
program execution begins.
A Sample C Program
/* Letter guessing game */
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
main()
{ int tries = 0;
char compAns, userGuess;
/* Save the computer's letter */
srand(time(NULL)); /* Randomize the number generator */
compAns = (rand() %26) +65; /* generate a random letter */
printf("I am thinking of a letter...");
...
A Sample C Programdo {
printf("What is your guess? ");scanf(" %c", &userGuess);tries++; /* Add 1 to the guess counter */
if (userGuess > compAns){ printf(" Your guess was too high \n"); printf(" \n Try again ...");}if (userGuess < compAns){ printf(" Your guess was too low \n"); printf(" \n Try again ...");}
} while (userGuess != compAns); /* Quit when a match is found */
/* User got it right, announce it */
printf("*** Congratulations! You got it right! \n");printf("It took you only %d tries to guess.", tries);return 0;
}
The Library and Linking
All C compilers come with a standard C library of functions
that perform most commonly needed tasks.
When you call a function that is not parf of your program,
the C compiler “remembers” its name. Later, the “linker”
combines the code you wrote with the object code
already found in the standard library. This process is
called linking.
Separate Compilation
C allows a program to be contained in many files and lets
you compile each file separately.
The advantage of separate compilation is that if you
change the code of one file, you don’t need to recompile
the entire program.
The Terms
• Source Code; The text of a program that a user can read. The source code is input in to the C compiler.
• Object Code; Translation of the source code of a program into machine code, which the computer can read and execute directly. Object code is the input to the linker.
• Linker; A program links separately-compiled functions into one program.The output of the linker is an executable program.
• Library; The file containing the standard functions that your program may use. (all I/O operations, useful routins..)
SourceCode Compiler Object
Code LinkerExecutable
program
Basic Data Types
Data types;• char• int• float• double
Type ApproximateSize in Bits Minimal Range
char 8 -127 to 127
unsigned char 8 0 to 255
int 16 -32767 to 32767
unsigned int 16 0 to 65535
signed int 16 same as int
short int 16 same as int
long int 32 -2,147,483,647 to 2,147,483,647
unsigned long int. 32 0 to 4,294,967,295
float 32 Six digits of precision
double 64 Ten digits of precision
long double 128 Ten digits of precision
Modifiers;• signed• unsigned• long• short
(long float has the same meaning as double).
Variables
• A variable is a named location in memory that is used to
hold a value that may be modified by the program.
• All variables must be declared before they can be used.
• General declaration form is;
type variable_list;
Example;
int i, j, l;
unsigned int u;
double balance, profit, loss;
Declaration of Variables
Variables will be declared in three basic places;
1. inside functions local variables
2. in the definition of function parameters formal
parameters
3. outside of all functions global variables
Sample – local variables
/* Addition */
#include <stdio.h>
#include <stdlib.h>
main()
{ int a, b, c;
printf(“\n insert a = %d”);
scanf(" %d", &a);
printf(“\n insert b = %d”);
scanf(" %d", &b);
c = a + b;
printf(“\n a + b = %d”, c);
}
Sample – formal parameters/* Addition */#include <stdio.h>#include <stdlib.h>int addition(int x, int y);main(){ int a, b, c;
printf(“\n insert a =”);scanf(" %d", &a);printf(“\n insert b =”);scanf(" %d", &b);c = addition(a, b);printf(“\n a + b = %d”, c);
}int addition(int x, int y) {
int z;z = x + y;return(z);
}
Sample – global parameters/* Addition */
#include <stdio.h>
#include <stdlib.h>
int a, b, c;
void addition( );
main()
{ printf(“\n insert a = “);
scanf(" %d", &a);
printf(“\n insert b = ”);
scanf(" %d", &b);
addition();
printf(“\n x + b = %d”, c);
}
void addition( ) {
c = a + b;
}
Local Variables
void func1(void)
{
int x;
x = 10;
}
void func2(void)
{
int x;
x = -199;
}
void f(void)
{
int t;
scanf(“%d”, &t);
if (t==1) {
char s[80];
printf(“enter name:”);
gets(s);
.... /* do something */
}
}
#include “stdio.h”
void f(void)
void main(void)
{
int i;
for(i=0; i<10; i++) f();
}
void f(void)
{
int j = 10;
printf(“%d”, j);
}
Formal Parameters
• If a function is to use arguments, it must declare variables that will accept the values of the arguments. These variables are called the formal parameters of the function.
/* Return 1 if c is part of string s; 0 otherwise */
is_in(char *s, char c)
{
while (*s)
if (*s==c) return 1;
else s++;
return 0;
}
Global Variables
#include “stdio.h”
int count; /* count is global */
void func1(void);void func2(void);
void main(void){
count = 100;func1();
}void func1(void){
int temp;temp = count;func2();printf(“count is %d”, count);
}
Global variables are known throughout the program and may be used by any piece of code.
void func2(void){
int count;for (count=1; count<10; count++)
putchar(‘.’);}
const• Variables of type const may not be changed by your program. • A const variable can be given an initial value.
const int a = 10;#include “stdio.h”void sp_to_dash(const char *str);
void main(void){ sp_to_dash(“this is a test”);}
void sp_to_dash(const char *str){ while (*str) {
if (*str==‘ ‘) printf(“%c”, ‘-’);else printf(“%c”, *str);str++;
}}
#include “stdio.h”void sp_to_dash(const char *str);
void main(void){ sp_to_dash(“this is a test”);}
void sp_to_dash(const char *str){ while (*str) {
if (*str==‘ ‘) *str=‘-’;printf(“%c”, *str);str++;
}}
Operators• The assignment operator;
variable_name = expression;
The target, or left part of the assignment must be a variable or a pointer, not a function or a constant.
• Multiple assignment ; x = y = z = 0;• The conversion assignment;
When variables of one type are mixed with variables of another type, a type conversion will occur.
int x; char ch; float f;
void func(void)
{ ch = x;
x = f;
f = ch;
f = x;
}
Common type conversion (Samples)
Target Type Expression Type Posssible info loss
char short int High order 8 bits
char int High order 8 bits
int long int High order 16 bits
int float Fractional part
float double Precision, result rounded
Arithmetic Operators
Operator Action
- Subtraction
+ Addition
* Multiplication
/ Division
% Modulus
-- Decrement
++ Increment
Relational or Logical OperatorsRelational Operators
Operator Action
> Greater than
< Less than
>= Greater than or equal
<= Less than or equal
== Equal
!= Not Equal
Logical Operators
Operator Action
&& AND
|| OR
! NOT
In C, true is any value other than zero. False is zero.
Logical Operators
AND
p q p&&q
0 0 0
0 1 0
1 0 0
1 1 1
OR
p q p || q
0 0 0
0 1 1
1 0 1
1 1 1
NOT
p !p
0 1
1 0
Sample for Logical Operations
#include “stdio.h”
int xor(int a, int b);
void main(void)
{ printf(“%d”, xor(1, 0));
printf(“%d”, xor(1, 1));
printf(“%d”, xor(0, 1));
printf(“%d”, xor(0, 0));
}
/*perform logical XOR operation using the two argumants. */
int xor(int a, int b);
{
return (a||b)&& !(a&&b);
}
a b a XOR b
0 0 0
1 0 1
0 1 1
1 1 0
Lab. Exercise #1
• Write a program that implements SWAP
operation for two integer variables
– with using a temp space,
– without using a temp space.
Next Course
Program Control Statements• Selection
– if and switch
• Iteration
– while, for, do-while
• Jump
– break, continue, goto, return
• Label
• Expression
• Block
– A block begins with a { and ends with a }.
