IT 3210 - C programming language

Algorithm

Set of instructions specifying the steps required to accomplish a task

Components of an algorithm

1. Variables and values

2. Instructions:

• Sequences

• Selections

• Iterations

• Procedures

(computer) Program

A sequence of instructions aims at solving a specific task

→ Instruction is carried out one after the other, none carried out when the previous isn’t accomplished

Interpreted & compiled language

• Interpreted: translated during execution

• Compiled: translated before execution

Values

Represent quantities/ amounts/ measurements

Variables (definition) 

Containers/ places to store values

→ Can be restricted to contain a specific type of value

Sequence structure

Series of instructions to be carried out one after the other

Selection

An instruction that decides which of two possible sequences is executed

→ Based on a condition (true/false)

• if …

• then …

• else …

Iteration

Repeat an instruction while/ until some true or false condition occurs.

→ Two kinds of iteration: Test the condition each time before/ after repeating the instruction

Procedure

A series of instructions with a name

→ divide a program into smaller parts with different names

C Language Structure

• #include <stdio.h> → To declare using the standard I/O library

• int main() → To declare the main() function → only one

• { … } → The syntax to open and close a block of codes.

• return 0; → Stop the program

Syntax

• Keywords: reserved words for specific meaning

• User’s names: defined by user to specify a variable, a function

• Specific characters: represent expressions in a program and make it have structure

Common used characters

• {…} create a block of instructions

• “…” create a string to display

• /* … */ create a block of comment in the program

• ; End of an instruction

• other characters for formulas such as +, -, *, /, (),

Identifier

When declare a variable/ procedure

Variable

• has a name (identifier)

• has types

• declared at the beginning of a function: <data type> <variable list>; → Assignment = puts a specified value into a specified variable

Basic data types

• char

• short

• int

• long

• float

• double

Strings

Groups of char form strings

→ must be enclosed by double quote “ ”

Logic

every number give also a boolean value

• 0 for false

• 1 for true

Const declaration

A variable declaration with the prefix const indicates that the value of that variable never changes in the program.

Data input/ ouput

• printf()

• scanf()

Formatting with printf

specify the field width by following:

% [-] [fwidth] [.p] X

• [fwidth] the field width

• [-] left justified

• [.p] the number of decimal places/ how many characters are to be printed

Expressions

• Combine values using operators, function calls

• Return a value of a known type 

Operator

Take values & do something to produce a result 

Operand

Operated upon by an operator

Arithmetic operators

• + (unary plus)

• - (unary minus)

• + (addition)

• - (subtraction)

• * (multiplication)

• / (division or quotient)

• % (modulus or remainder)

Comparison operators

• < (less than)

• <= (less than or equal)

• > (greater than)

• >= (greater than or equal)

• == (equal)

• != (in-equal)

Logic

• Have 2 values: true (1) ; false (0)

• Create the selection of conditions/ the loop for an algorithm

Logic operators

• && (and)

• || (or)

• ! (not)

• comparison (==, !=, <, >, <=, >=)

Bit operators

• & (and bit)

• | (or bit)

• ~ (negation)

• >> (shift right)

• << (shift left)

Short-circuiting

A complex Boolean expression is only evaluated as far as necessary

Extend assignment operators

• +=

• -=

• *=

• /=

• %=

Increment, decrement operators

• ++ is the increment operator

• -- is the decrement operator

→ Two ways of writing: prefix (++i) and suffix (i++):

• Prefix return value after adding 1

• Suffix return value before adding 1

• In both cases, value of i increases by 1

Conditional Expressions

<Condition> ? <Expression 1> : <Expression 2>

Casting data type

int a;

float f;

a = (int) f;

Precedences

• Unary operators (!, -)

• Multiply, divide (*, /, %)

• Addition, subtraction (+, -)

• Comparison 1 (<, <=, >, >=)

• Comparison 2 (==, !=)

• And (&&)

• Or (||)

• Assignment (=)

if statement

if ( expression )

statement

Statements

lines of instructions in programs ending with a semicolon (;).

• A compound statement/ block: series of statements surrounded by braces.

• An empty statement: a single semicolon.

else statement

if ( expression )

statement1

else statement2

• only occur after an if statement

• only executed when the if block does not execute

Cascading if (else-if)

if (expr1)

statement1

else if (expr2)

statement2

else if (expr3)

statement3

else

statement4

• At most only one block will be executed

• Choose one among several conditions

switch statement

switch (integer value)

{

case 1: statement1;

break; /* optional line */

case 2: statement2;

break; /* optional line */

....

default: default statement;

break; /* optional line */

}

• The expression in the parentheses is evaluated

• Check to see whether the result matches any constants labelled with case

• A match is made → execution start after that case statement → carry on until the closing brace } / break statement

• Default case are executed for all cases not specifically listed

Using break

All following statements are carried out until a break statement

→ break is a way of jumping straight out of the switch block

Loop

Repeat statement(s)

→ Provide versatile manipulation:

• number of repetitions

• range of loops

while loop

while ( condition(s), )

statement(s)

• Execute a statement according to a condition

• Verify the condition at the beginning of the loop

• Stop the loop when the condition is false ( = 0 )

for loop

for ( initialization ; condition ; update )

   statement

• All components are optional → If the condition is empty, interpreted as true

• (,) separates elements of a component

do … while statement

do {

statements;

} while ( condition);

→ The loop always executed at least once before the test → determine whether it should continue

Infinitive loops

The loop condition is always true

• while (1)

• for (;;)

Break statement

Use in an infinitive loop to terminate the loop

→ for (;;)

{ …

if (condition) break;

}

Continue statement

A loop will stop whatever it is doing → go straight to the start of the next loop pass

→ for (…)

{…

if ( condition) continue;

…}

build function

specify

• function name

• input parameters

• type of value returned ( if exists)

• block of statements executed when function is called → function body

function parameter

local variable of a function whose parameter is determined each function call

→ no parameter → use void

return statement

return a value

→ may have multiple returns → first one encountered terminates the others

function declaration & definition

• definition: specify all components

• declaration: specify name, type of parameter, return type → function prototype

global & local variable

• global: declare outside function → accessed by multiple functions

• local: declared inside a function → accessed only in that function
  → name conflict → local variable takes precedence

Array

block of variables that have the same datatype → fixed number of elements

Pointers

variable that can store the memory of another

→ format specifier: %p

How to use pointer

• declare variable pointed to by pointer: int num

• declare pointer: int *numPtr = NULL;

• assign reference to pointer: numPtr = &num;

• dereference pointer: *numPtr = 65;

String processing

• assignment( copy): strcpy ()

• concatenation: strcat ()

• comparison: strcmp ()

• get strign length: strlen ()

string comparison

strcmp (string1, string2)

→ lexicographically compare

result:

• = 0 → equal

• > 0 → string 1 > string 2

• < 0 → string 1 < string 2

Struct

collection of variables

struct nameOfstruct {

};

→ names of variables inside struct: struct fields/ members

→ access a field: use . → nameOfstruct.variableName

typedef

define new data type name that can be used in variable declaration

input/ output stream

buffered area used for high-level data input, output

→ 3 standard streams:

• stdin: input

• stdout: output

• stderr: error