Introducing programming

March 24

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Program structure Statements to establish the start of the program Variable declaration Program statements (block statements)

Operators Arithmetic operators Logic operators Bit operators Comparison operators

Conditional statements Branching statements

Implemented in ALU in CPU

Implemented in Control Unit in CPU

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Start of the program

beginning

end

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Hello world in different languages

C language Pascal language

C++ language Java language

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Flowcharts and C language

Start / stop

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

}

printf(“number %d”, 5);scanf(“%d”, &num);Input / Output

conditiontruefalse

if( condition ){//true

}else{//false

}

Computations int area = pi * r * r;

A Simple program

Use the .2 modifier to the %f specifier to fine-tune the appearance of the output so that it displays two places to the right of the decimal.

To provide keyboard input to the program, use the scanf() function. The %f instructs scanf() to read a real number from the keyboard, and the &weight tells scanf() to assign the input value to the variable named weight.

Interactive program The interactive approach makes programs more flexible; The sample program can be used for any reasonable weight; The scanf() and printf() functions make this interactivity

possible.

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The largest of two numbers

start

read X, Y

output X

stop

X > Y ?

output Y

stop

yes no

the program starts here

read x,y

the program ends here

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Variables Variables are place holders for data a program might use or

manipulate. Variables are given names so that we can assign values to them

and refer to them later to read the values. Variables typically store values of a given type.

Integer – to store integer or “whole” numbers: 512, -123 Real – to store real or fractional numbers (also called float to

indicate a floating point number): 3.14, 2.7 Character – A single character such as a letter of the alphabet or

punctuation: ‘a’, ‘!’ String – A collection of characters: “Hello world!” Structure – A compound user defined type: student{name, id}

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Basic Data TypesMost of data types are formed from one of the four basic arithmetic type specifiers in C

char is used to store characters, generally occupies 1 byte of memory Int is used to store integers, occupies at least 2, but usually 4 bytes float is used to store real values with single precision double is used to store real values with double precision

and optional specifiers signed specifies that negative and positive values can be stored (only for integers) unsigned specifies that only non-negative values can be stored (only for integers) short short signed integers long long signed integersExamples

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A few rules about naming the variables Characters allowed

Underscore _ Capital letters A-Z Small letters a-z Digits 0 – 9

First character should be alphabet or underscore Blanks, commas and symbols are not allowed Variables name should not be reserved word

num_1NumNum1_NUMNUM_temp2

Valid names:

number_of_valuesInteger_num1Num___

Valid names: Invalid names:

1num1_num365_days@namechar

Some programming languages following these rules are C, C++, Java, Python, PHP

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Variables C

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Variables are declared; Memory will be allocated at the execution time

Variables are initialized

In order to use a variable within a program, the compiler needs to know in advance the type of data that will be stored in it.

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VariablesJa

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Variables are declared; Memory will be allocated at the execution time

Variables are initialized

Variable declaration consists of giving a new name and a data type for the variable

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Operators Arithmetic Comparison operators/relational operators Logical operators Bitwise operators Compound operators Member and point operators

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Basic arithmetic operations In order to use a variable within a program, the compiler needs

to know in advance the type of data that will be stored in it.Operator name Syntax Example

Basic assignment a = b x = 5;

Addition a + b x = x + 5;

Subtraction a - b x = 4 – y;

Unary plus +a x = +5 ;

Unary minus -a x = -5;

Multiplication a* b x = x * y;

Division a / b x = x / y;

Modulo (integer remainder) a % b x = 10 % 3

Increment Prefix ++a x = ++5; // x will be 6

Postfix a++ y = x++; // y = x; x = x + 1;

Decrement Prefix --a x = --5; // x will be 4Postfix a-- y = x--; // y = x, x = x - 1

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Examples

Arithmetic operators: remainder In arithmetic, the remainder is the amount "left over" after

the division of two integers which cannot be expressed with an integer quotient.

The general form of a linear equation can be expressed as a = q * d + r.

q is the quotient and d as the divisor, r as the remainder.

r = a - q * d.

For example: a = 810, q = 3, d = 256, r = 42But we only know a and d and we want to find q and r.a / d = 3.1640625 q = [a / d] = 3 and r = 810 – 3 * 256 = 42

Arithmetic operators: Using % op. The program converts a given number of days into months and days

Arithmetic operators: Using % op.

Increment and decrement operators

C allows two very useful operators not generally found in other languages. There are the increment and decrement operators: ++ and --

The operator ++ adds 1 to the operand, while -- subtracts 1.

++m; is equivalent to m = m + 1; (or m+= 1)

--m; is equivalent to m = m -1; (or m-= 1)

m = 5;y = ++m;

m = 5;y = m++;

Prefix operator Postfix operator

m is 6 and y is 6 m is 6 and y is 5

• Example: m = n++ - j + 10; Old value of n is used in evaluation.

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Basic logical operatorsIn Boolean logic, the operands are statements (that can be proven True or False) and the operators are logical AND, OR and NOT. Example:

I am 6 feet tall AND I am president of the United States While it may be True that he is six feet tall (a fact that can be proven

by measuring my height), it can certainly be shown that he is not the president of the United States. Therefore, according to Boolean logic, this entire sentence is False.

I am 6 feet tall OR I am president of the United States In this case that only one of the parts of the sentence (separated by

OR) need be True in order for the entire sentence to be considered True.

It is True that I am 6 feet tall OR I am the president of the United States.

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Basic logical operators There are three Boolean operators: AND, OR and NOT. These

operators are written differently depending on the language being used. In mathematics, the logical operators are written as

Operator Name Syntax Math notation

Logical negation (NOT) ! A

Logical AND a && b

Logical OR a || b

Bitwise operatorBitwise operators are used for testing the bits, or shifting them right or left. Bitwise operators are not applied to float or double.

Operator Meaning

& Bitwise AND

| Bitwise OR

^ Bitwise exclusive OR

<< Shift left

>> Shift right

inputs &

0 & 0 00 & 1 01 & 0 01 & 1 1

inputs |

0 | 0 00 | 1 11 | 0 11 | 1 1

inputs ^

0 ^ 0 00 ^ 1 11 ^ 0 11 ^ 1 0

Digital logic notation:

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Example of bitwise operators

Checks if bit 3 (corresponds to 4 in decimal system) is on

Remember: 1 1 1 1 1 1 1 1 (binary system)128 64 32 16 8 4 2 1 (decimal system)

Checks if bits 1 and 2 (corresponds to 5 in decimal system) are on

Sets bit 1 (corresponds to 1 in decimal system) to on

Sets all bits that are different to on00000010 ^ 00000101 = 00000111

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Example of shifting operators

equivalent to multiplication by 2

equivalent to division by 2

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Comparison operators/ relational operators Boolean expressions often involve comparison operators that

can be evaluated to determine if they are True or False.

Operator name Syntax

Equal to a == b

Not equal to a != b

Greater than a > b

Less than a < b

Greater than or equal to a >= b

Less than or equal to a <= b

Example: Question ExpressionDoes Alice make more than $35,000 per year? Alice_Salary > 35000Did the NY Giants defeat the Dallas Cowboys? Giants_Points > Cowboys_Points

Did anyone get a perfect score on the test? TestScore == 100

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Comparison operators/ relational operators

A simple relational expression contains only one relational operator:

arithm_expr1 relat_op arithm_expr2 4.5 <= 10 TRUE 4.5 < -10 FALSE -35 >= 0 FALSE 10 < 7+5 TRUE

a + b == c + d TRUE // if a + b is equal to c + d

Relational operators: Example For example you have 1000 Won in your

pocket, then when the question is: Do I have enough money to buy an ice

cream In C this question can be written as follows

YES (TRUE) any non-zero value

NO (FALSE)

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Combining Boolean and Comparison Operators

The two types of operators are used to form more complex expressions. Ex.: Are there more than 30 students in the class, and are there more

than 30 seats in the room?Number_of_Students > 30 AND Number_of_Seats > 30

Compound expression

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Conditional Statements Control statements “control” which sections of code in a

program are executed There are three general types of control statements:

Sequential – The default ordering of execution Decision (Conditional) – controls which block of code within

several alternatives is executed. Iterative – controls how many times a block of code is executed.

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Decision (Conditional) Decision or Conditional statements are a type of Control

statement and are often referred to as IF..THEN..ELSE statements

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Iterative Constructs (Loops)All programming languages have a facility to allow a section of code to be repeated (iterated or looped). There are several variations:

for loop: for (initialization; condition; increment){…}

while loop: while (condition){statements}

do while loop: do{statements}while (condition)

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Recall: The largest of two numbers

start

read X, Y

output X

stop

X > Y ?

output Y

stop

yes no

the program starts here

read x,y

the program ends here

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Larger of three numbers

start

read X, Y, Z

stop

X > Y ?

stop

yes no

max > Z ?

Output max Output z

yes no

Max = X Max = Y

Transform the flowchart below to a C language program.

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Find whether a number is odd or even Draw a flow chart for the algorithm that checks whether the

number is odd or even. Convert the algorithm into C language program

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Example of a while loop The program prints out a conversion table from Fahrenheit to

Celsius. Draw a corresponding flowchartProgram Output

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start

read N

stop

Count > N ?

output sum

no yes

sum = sum + count * count

sum = 0count = 1

count = count + 1

Example of a for loopThe program calculates sum = 12 + 22 + 32 + … + N2

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start

read N

stop

Count > N ?

output sum

no yes

sum = sum + count * (count + 1)

sum = 0count = 1

count = count + 1

sum = 1 * 2 + 2 * 3 + 3 * 4 + … + N* (N +1)Convert to C program

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start

read N

stop

count > N ?

output sum

no yes

prod = prod * count

prod = 1count = 1

count = count + 1

Computing factorialConvert to C program

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start

Read X, N

stop

count > N ?

output sum

noyes

sum = prod * countterm = term * X / count

term = 1prod = 1count = 1

count = count + 1

Computing ex series up to N terms

Use Taylor expansion to represent ex up to N terms.

Convert to C program

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start

Read X, N

stop

term < .0001 ?

output sum

noyes

sum = prod * countterm = term * X / count

term = 1prod = 1count = 1

count = count + 1

Computing ex series up to 4 decimal places

Use Taylor expansion to represent ex up to 4 decimal places.

Convert to C program