Assoc. Prof. Dr. Tansu FİLİKeem.eskisehir.edu.tr/tansufilik/BİL 200/icerik/Bil200_Week_6.pdf · Arrays Computer Programming Arrays It is the declaration of a list of same type

Assoc. Prof. Dr. Tansu FİLİK

Previously on Bil 200

Computer Programming

Midterm Exam - 1

Arrays


ArraysList of variables: [ ]

Arrays


Arrays

It is the declaration of a list of same type of

variables under a single name.

An example can be the days of week. This is

a 1-D array. The first element is Monday, the

last is Sunday.

Arrays


Arrays

Another example is the days of a month. This can be considered as a 1-D array, or a 2-D array whose horizontal elements are days of weeks, and vertical elements are the weeks.

Days of a year, therefore, can be considered as a 3-D array. First dimension is days of week, second dimension is weeks of month, third dimension is months of year.

Arrays


Array declarations

A 1-D array is declared by a variable name and number of elements inside a square bracket.

Example:

int gun [ 7 ];

gun corresponds to the array name, whose elements are of int type. There are seven elements.

Similarly, a 2-D array is declared by two square brackets:int ay[ 4 ][ 7 ];

There are 4 rows and 7 columns of ay.

Arrays


Array usage

Each element of an array is reached by its

index written in square parantheses.

In C, the first element is with index 0 (zero). For example, the gun array has first 0th, and

last 6th element.

The numbers inside the square parantheses

are called index numbers.

Arrays


gun[0] gun[1] gun[2] gun[3] gun[4] gun[5] gun[6]

2 6 6 4 12 54 -10

int gun[7];

gun[5] = 1;if( gun[5] == 4 ) break;gun[5] = gun[6] - 1;

Usage examples:

Arrays


Example#include <stdio.h>

void main()

{

int gun [ 7 ];

int i;

for( i = 0 ; i < 7 ; i++ )

{

gun[ i ] = 0;

}

}

Arrays

int c[12];

c[0]=-45;

c[1]=0;

c[2]=6;

....

c[11]=78;

c[6]

-45

6

0

72

1543

-89

0

62

-3

1

6453

78

c[0]

c[1]

c[2]

c[3]

c[11]

c[10]

c[9]

c[8]

c[7]

c[5]

c[4]

The array index starts from 0.

and ends at N-1

Bil-200

x=2;

c[x] == c[5-3] == c[2] == 6;

typical mistakes:

c(4)

c[1] ... c[12]

float f=1.0;

c[f];

Arrays

Bil-200

Arrays


Initializations of arrays

We know how to initialize single variables while declaration. The situation is similar for arrays. Just use a list o values inside a block separated by “,”s.

#include <stdio.h>

void main()

{

int gun[7] = { 0,2,4,6,8,10,11 };

..........

}

Arrays


Initializations of arrays

If the array size is too big, declarative initialization is difficult. In that case, make initial assignments inside a program using loops. If we still want to make initializations, we may initialize the first few, and the rest will be zero. As an example:

int sayilar [ 10 ] = { 2 };

double dizi [ 250 ] = { 0 };

Arrays - Example


#include <stdio.h>

void main()

{

int gun[7] = { 2,3,4,5,6,7,8 };

int i;

for (i = 0 ; i < 7 ; i++ ) {

printf ("gün[%d] Şubat %d, 2004\n", i, gun[i] ) ;

}

}

Arrays - Example


Write a program which generates random numbers as many as required by the user.

The random number generation function exists in a standard library called "stdlib.h". The function name is rand(). It generates numbers between 0 and 32767.

In order to randomize the generation, use fhefollowing function: "srand(time(NULL));".

The function “time( )” requires including "time.h".

Arrays – Example: Solution


#include <stdio.h>

#include <stdlib.h>

#include <time.h>

#define UZUNLUK 10

void main ( )

{

int i, sayilar [UZUNLUK] ;

srand(time(NULL));

for (i = 0 ; i < UZUNLUK ; i++ ) {

sayilar[ i ] = rand ( ) ;

printf ( "sayi [ %d ] = %d\n", i, sayilar[ i ]) ;

}

}

Arrays – Exercise


How do we generate 100 random values

using the previous program structure?

Extend the program so that it finds and writes

the maximum and minimum values inside

the random array. Furthermore, the program

must find the average, too.

Exercise Write the following program and see that the result is NOT

1.00000

#include <stdio.h>void main(){

float top = 0.0;int i;

for(i=0;i<10000;i++) {top += 0.0001;

}printf("toplam = %f\n", top);

}

It will display1.000054 on the

screen.

Why?

Floating point numbers are not exactly realnumbers.

Floating point numbers are represented byinverse powers of 2 (binary representation).

Each 0.0001 will not be precisely 0.0001, sowhen we add them 10000 times, the result willbe different.

For a better precision, use double. But it will costmore memory.

Rounding errors

In floating points, never use equality comparisons.

for (x = 0.0; x != 10.0; x += 0.1) {

…

}

Use “near” comparisons for floating points.

In some computers, the following code will result in different number of loops!

for (x = 0; x < 10.0; x += 0.1) {

…

}

For loops, prefer integers.

int and char

int (32 bit) and char (8 bit) may also be casted to

each other.

int char_kod;

for (char_kod = (int) 'A'; char_kod <= (int) 'Z'; char_kod++) {

printf("%c", (char) char_kod);

}

This program prints out ABCDEFGHIJKLMNOPQRSTUVWXYZ

on the screen.

C Libraries

Introduction to Programming Languages

C Liabraries"math.h", "stdlib.h", "string.h"

C Libraries


The main C language only consists of expressions

and grammar rules. C, itself, has NO built in

function!

Most C compilers come with the standard libraries

containing several useful functions.

In order to be able to use these functions, you must use #include directive to include the associated

library containing the useful function.

C Libraries


Function Libraries

<stdio.h> - printf(), fprintf(), scanf(),

fscanf(), fopen(), putchar(), getchar(),

....

<math.h> - pow(), sqrt(), fabs()...

<ctype.h> - toupper(), tolower(),

isalpha(), isdigit(), ....

<stdlib.h> - rand(), srand(), exit(), ....

C Libraries


Function Libraries : math.h Many mathematical function (prototypes) exist here.

fabs (x) : absolute value of float x

sqrt (x) : square root of x

exp (x) : e to the power x (e = 2.71828)

log (x) : ln x

log10 (x) : base-10 logarithm

pow(x, y) : x to the power y

sin (x) : sine (radians)

cos (x) : cosine (radians)

tan (x) : tangent

fmod (a, b) : remainder of a/b

ceil (x) : least integer >= x

floor (x) : greatest integer <= x

C Libraries


Function Libraries : stdlib.h exit(val) : used for terminating program.

if (fp == NULL)

exit(1); /* if file cannot open, quit*/

rand(void) : generates a random number

for(i=0; i < 100; ++i) /* 100 random numbers*/

printf("%d ", rand());

srand(value) : seed for the randomizer

srand(100); /* starting point of random sequence*/

C Libraries


Function Libraries : time.h

time(NULL): Numbe of seconds passed since

01/01/1970.

int secs;

secs = time(NULL);

C Libraries


Example: Approximate pi value

Pi is a very commonly used constant in mathematical expressions.

This number has infinite decimal points. Special applications require as many of these decimals as possible. Simple applications may be OK with 22/7.

In the following example, we will see how near to pithe value 22/7 is.

In C, asin(1) is approximately equal to pi.

Approximate value of pi

#include <stdio.h>#include <math.h>

int main(void) {

double pi, yak, hata;

pi = 2 * asin(1); /* realistic pi value*/yak = (double) 22 / 7; /* approximate pi */hata = fabs(yak – pi) / pi; /* find error */

printf("pi = %.15f\n", pi); /* write result */printf("yaklaşık = %.15f\n", yak);printf("hata = %.5f", hata * 100);

return 0;}

asin, is the arc-sine

function.

pi = 3.141592653589793

yaklaşık = 3.142857142857143

hata = 0.04025

Press any key to continue

time(NULL)

Gives number of seconds since 01/01/1970 At 13:40 on 17/11/2015, its value was.

zaman: 1447760273

#include<stdio.h>

#include<time.h>

void main(){

int t;

t = time(NULL);

printf("zaman: %d \n", t);

}

time(NULL)

Before using you should write:

#include <time.h>

Usage:

int t;

t = time(NULL);

Since each time instant is different, it

is a good randomization seed.

Clock: tik-tak

#include <stdio.h>#include <time.h>

void main(void) {

int i, t;

for(i=0; i <= 10; ++i) { /* just for 10 sec */t = time(NULL) + 1; /* t next sec */

while (time(NULL) < t); /* wait */printf("tik\n"); /* write tik */

t = time(NULL) + 1; /* wait 1 sac */while(time(NULL) < t); /* wait */printf("tak\n"); /* write tak */

}}

Functions


FunctionsThe modules that are written by the programmer

Functions


Function Calls

Calling a function means “returning the value of a named list of commands that do a specific task”.

We may call functions that we write ourselves.

We may call functions that already exist in the standard C library.

Ex: printf, scanf, sqrt

Functions


Example

Write a program which

obtains and prints out

the square-root of an

entered number.#include <stdio.h>#include <math.h>/* Ekrandan girilen bir

sayının karekökünüyazar. */

int main(){

float x, sonuc;printf("Bir sayi giriniz"); scanf("%f", &x);

sonuc = sqrt(x);printf("Sonuc = %f", sonuc);return 0;

}

Functions


Until now, we wrote our program using a single function: main().

The sytax was:

void main ( )

{

/* definitions */

/* expressions */

}

The term void indicates that this function returns NOTHING.

Functions


The () parantheses indicate that main is a function. Inside these parantheses, you send parameters to the function. For this particular case, we do not send anything to the function, so the parantheses are empty.

Normally, functions require a list of parameters to be sent to them for processing and generating a result. That result may be returned to the function calling place.

Functions


A function can be written is three steps:

1. Function prototype declaration

2. The function itself (declaration + commands

inside)

3. The expression that calls the function.

Functions


1. Function prototypes

Compilers trace the program from top to bottom. If you write

a program which tries to use your functions, the compiler

needs to know “how” the function is called.

The prototypes are listed at the top to show the parametric

interface of functions.

void, char,

int, float,

double

semicolon

Functions


1. Function prototypes: Parameters

Parameter list is a list of types that will enter to the

function.

float toplam(int a,int b,int c) ;

Functions


2. Function definition

In the real declaration of function, do not put ; at

the end of first line.

float toplam(int a,int b, int c)

Here, the function toplam takes three variables: a, b

and c. The return type is float.

a, b and c values are sent by the place where the function is called.

Functions



Function definition consists of a declaration line similar to the prototype, followed by a list of commands bounded by curly parantheses:

float toplam( int a, int b, int c)

{

float t;

t = a + b + c ;

return t;

}

Note: The function returns a value using the return keyword. If the return type is void, you do not need to use a return line.

Functions



float toplam( int a, int b, int c)

{

float t;

t = a + b + c ;

return t;

}

The variables a, b and c are valid only inside the function toplam.

The variable t is also valid only inside the function, and its

memory location is freed when the function finished.

Functions


3. Function calls

While calling a function, it must be compatible with the prototype and the return type. The sent parameters must also be compatible with the types. You may send proper variables, expressions, or values to a function. For this case:

deger = toplam( i, j, k ) ;

or

deger = toplam( 5, x, 2.7 ) ;

Functions


3. Function calls

Inside the main() function, the function toplam() is called. In that case, the parameter values are copied into the parameter list variables of the function.

Functions


3. Function calls

main() data memory

12

i

25

j

45

k

toplam() data memory

copied

copied

copied

12

a

25

b

45

c

FUNCTIONS- review#include<stdio.h>void func1(void);int func2(int n, char ch);void main(void){

int i=1,j=2;char ch=‘0’;printf(“%d %d\n”,i,j);func1();j=func2(i,ch);printf(“%d %d\n”,i,j);

}void func1(void){

printf(“selam!\n”);}.......

Prototype declarations. Before using in main or other functions, declare their names like this.Their bodies will be written later.

Calling a void-type function. Result is not assigned to anything.There is no input (void).

Function generates an int type output.Therefore, its output can be assigned to somevariable. Inputs are an int and a char.

One of the functions whose prototype wasdeclared. It is fully defined here. The I/O style of this and its prototype are compatible.

....

int func2(int x, char y)

{

int z;

printf(“Basta: x=%d, y=%c\n”,x,y);

z=x*y;

printf(“Simdi: z=%d\n”,z);

return z;

} /* As a result, this function adopts a value at the place

where it is called. */

Since function generates an int ...

...an int variable is declared inside ...

...and a value is assigned to it ...

...and variable is returned (function value produced).

Functions


Prototypes are necessary if you plan to write

functions at the end of the program. In this way,

you can safely use functions within functions.

If you write functions before main, or before other

functions which call them, you do not need to use

prototypes.

In this case, if a function (a) is used in function (b),

then (a) must be written on top of (b).

Functions


General function syntax

void face(void)

{

printf(“:-)”);

}

void next_line(void)

{

printf(“\n”);

}

void faces(int n)

{

if(i<=0)

return;

else

{

for(i=1;i<=n;i++)

face();

next_line();

}

}

void main(void)

{

faces(3);

faces(2);

faces(1);

}

:-):-):-):-):-):-)

Functions


Exercise: function factorial()

Write a function to evaluate the factorial of a

number. For parameters less than zero, the return

value will be 0. For zero and one, the return value is

1, for larger numbers, use a loop to evaluate.

In the main function, write a loop to evaluate

factorials of numbers from 0 to 10, and print on the

screen.

Do not forget to write the prototype.

Functions


Exercise: factorial program

#include <stdio.h>

int factorial( int x);

void main()

{

int i;

for (i = 0 ; i < 10 ; i++ ) {

printf("%d! = %d\n", i,

factorial(i));

}

}

Functions


Exercise: factorial program

int factorial ( int x )

{

int f = 1, k;

if ( x < 0 ) return 0;

else if ( x==0 || x==1 ) {

return 1; /* Return 1 for 0 or 1

*/

}

for ( k = 2 ; k <= x ; k++ ) {

f *= k ;

}

return f ;

}

Functions


Exercise:

Write a function which takes two parameters and

returns the factorial of the difference.

Function must start as:

int factorial_diff(int a, int b)

This function may call the function factorial()

which was previously implemented.

Do not forget to write the prototypes.

Functions


Class Exercise: Main Program

#include <.......>

/* prototype */

int factorial_diff(int a, int b);

void main()

{

int a,b;

printf("Farkın alinacagi sayilari girin: ");

scanf("%d %d", &a, &b);

printf("fark= %d\n", factorial_diff(a,b));

}

Functions - Phylosophy


For early programming languages, procedural

structure was a great improvement...

Instead of a single big and nasty program;

Intelligible and easily written blocks are preferable.

Then, which parts should be made a function? How

do we decide on the structure?

How do functions communicate with each other

and with main? There must be an interface

standard.

Documents

Assoc. Prof. Dr. Tansu FİLİKeem.eskisehir.edu.tr/tansufilik/BİL 200/icerik/Bil200_Week_6.pdf · Arrays Computer Programming Arrays It is the declaration of a list of same type