Computer Fundamentals NotesBy: Nida Afaq Warsi

BEE-3B

Variables

Variables are references that stand in for a value that is contained at a certain memory address. Variables are said to have a value and may have a data type.

Example:

Variable “X”

Each cell in the above diagram represents a memory location, and can be excessed through a memory address.

Each cell represents a unit of memory called a byte. Each byte consists of 8 bits. Eight bits is a convenient power of two allowing the values 0 through 255 to be stored on one

byte.(As 28 = 256, thus including 0 a total of 255 values can be stored) To store a value greater than 255, we combine two cells and treat them as a single number. Each cell can now store 255 values each thus a maximum value of 232-1 = 65535 can be stored

using two bytes.

Example:

Z= 28Y +X

X

ZX Y

The order in which this sequence of bytes is stored is called Little Endian. In this order the "little end" or the least significant value in the sequence is stored first. Thus “X” being the least significant is stored before “Y”.

Example:

To store the number Z = 1000 the value of X= 232 while Y = 3.

The table below shows some of the values of X and Y with the corresponding value of Z.

X Y Z0 0 01 0 1

255 0 2550 1 256

1 1 257

255 1 511255 255 65535

Variable

Name Example X,Y

Data Type Floating-point, integer, Double

Size Depends on the data typeExample integer value maybe 32 bits

Value Actual Content

*Note: Left hand side should have only variables.Example: Correct Expression:

Z=X+4

Incorrect Expression:X+4=Y+7

Expressing The Quadratic Formula in terms of the basic functions

Sum (a,b) = a+bProduct (a,b) = abSqrt (a) =√aDiv (a/b) = a/b

Root(a,b,c) = -b +√b2-4ac 2a

Div(Sum(Sqrt(Sum(Prod(b,b),(Prod(Prod(a,c),-4))))),Prod(b,-1))Prod(2,a)

Start from the center, in the above example from the product of a and c and work your way outwards.

Creating a function “add” with two input parameters and an output parameter

Add

+: x

The above symbols mean mapping from two sets of real number to one set. Function “add” is written in the beginning. Symbol “ ” Indicates that the two parameters to be added are real

numbers, and the resultant value is also a real number.

+: x

The above symbolic representation indicates that two integers add to give another integer.

Naming the function In C programming the function name has to start with a letter. Numbers

can than follow.Example: doc, A2,a23b, abc The letters maybe in uppercase or lowercase (Note C language is case

sensitive) There should not be any punctuation or spaces in the name of the function. Underscore can be used in the name if the function.

Example: add_two_numbers +: x

Data Types

Float and double are use to store real numbers.

Modifiers A type modifier alters the meaning of the base type to yield a new

type. Two modifiers: 1) Signed 2)Unsigned values.

Character (char) 8 bit integer value

Integer (int) 16 0r 32 bit integer value

Long 32 bit integer value

Float Simple

Double More precise

Signed and unsigned values We represent a number's sign by allocating one sign bit to represent

the sign: set that bit (often the most significant bit) to 0 for a positive number, and set to 1 for a negative number.

The remaining bits in the number indicate the magnitude (or absolute value). Hence in a byte with only 7 bits (apart from the sign bit), the magnitude can range from 0000000 (0) to 1111111 (127). Thus you can represent numbers from −127 to +127 once you add the sign bit (the eighth bit). A consequence of this representation is that there are two ways to represent zero, 00000000 (0) and 10000000 (−0)

Character I character has 8 bits thus occupies one cell of memory. Characters may also be signed or unsigned. Unsigned characters have values between 0 and 255, signed

characters have values from –128 to 127.

Integer Considering a 16 bit integer a maximum intrager value is 65535. A signed integer use one bit for storing sign and rest 15 bits for

number. Its value range limited to -32768 to +32767.

Long It is a 32- bit value

Float The float data type is used to store fractional numbers (real

numbers) with 6 digits of precision. Float is faster than double.

Double The double is same as float but with longer precision and takes

double space (8 bytes) than float. Double consumes more memory than float.

Analysing the Program

Program 1

#include <stdio.h>

int main(void){

printf (“Hello, world!\n”);return 0;

}

A function in C language is a block of code that performs a specific task. Every function has a unique name. This name is used to call function from

“main()” function. A function is independent and it can perform its task without intervention

from or interfering with other parts of the program. A function performs a specific task. A task is a distinct job that your program

must perform as a part of its overall operation, such as adding two or more integer.

A function returns a value to the calling program. This is optional and depends upon the task your function is going to accomplish. Suppose we want to just show few lines through function then it is not necessary to return a value.

But if you are calculating the sum of two numbers and wanted to use result somewhere in program then you have to send back (return) value to the calling function.

C language is collection of various inbuilt functions. If you have written a program in C then it is evident that you have used C’s inbuilt functions. Printf, scanf, clrscr etc. all are C’s inbuilt functions.

There are no parameters of the above function as it says (void).

The return type of this function is an integer since it says:

The text enclosed in quotation marks is called string. \n means new line Prototypes are often in a separate header file which can be included in other

C source files that wish to use the functions. The header stdio.h, for example, contains prototypes for the functions scanf and printf. The compiler will let us call those functions. The actual code for these functions is kept in a library elsewhere on the system, the header file only says how to interface with the functions.

Exit the function.

int main (void)

return 0;