Fundamental of Programming (C)

Lecturer: Omid Jafarinezhad

Sharif University of TechnologyDepartment of Computer Engineering 1

Fundamental of Programming (C)

Lecture 3Constants, Variables, Data Types, And Operations

Constants, Variables, Data Types, And Operations – Lecture 3


Outline• C Program• Data types• Variables• Constants• Operations

– Arithmetic Operators • unary operators

– operators that require only one operand• binary operators

– operators that require two operands

– Assignment Operators– Equality and Relational Operators– Logical Operators– Bitwise Operators – Conditional Operator– Comma Operator– sizeof



C Program

stdout (Screen)

stdin (Keyboard)

stderr (Screen)

Constants and variables

Operations and functions

main

X Y Z

A B C D

Instructions and operating procedures



Simple Program• Examples:// int is return data type// main is entrance functionint main(){ statement 1; statement 1; // …. return 0; }

/* Objective: print on screen*/#include <stdio.h> // preprocessor statements have not ;int main(){ printf("welcome to c!!!"); return 0; // indicate that program ended successfully }

welcome to c!!!

// Simplest c programint main(){ return 0;}



• Examples:– Header file– Main function– Variables– Input and output – Process

#include <stdio.h> // header file (preprocessor )// calculating sum of two user input variables int main(){ /* variable definition */ int a; int b; int result = 0; // get first variables form user printf("Enter first number:\n"); scanf("%d", &a); // get scoend variables form user printf("Enter scoend number:\n"); scanf("%d", &b); // sum of input variables result = a + b; printf("%d + %d = %d\n", a, b, result); system("Pause"); return 0;}



• Examples:– Header file– Constant– Main function– Variables– Input and output – Process

#include <stdio.h> // (preprocessor )

#define PI 3.14 // PI constant (preprocessor )

// calculating area of circleint main(){ /* variable definition */ float Radius; float Area = 0; // get radius of circle form user printf("Enter Radius :\n"); scanf("%f", &float ); // calculating area of circle Area = PI * Radius * Radius; printf(“Area = %f", Area );

system("Pause"); return 0;}






// calculating area of circleint main(){ /* variable definition */ float Radius; float Area = 0; // get radius of circle form user printf("Enter Radius :\n"); scanf("%f", & Radius); // calculating area of circle Area = PI * Radius * Radius; printf(“Area = %f", Area );




Variables• Have the same meaning as variables in algebra

– Single alphabetic character– Each variable needs an identifier that distinguishes it from the others

• a = 5• x = a + b

• valid identifier in C may be given representations containing multiple characters– A-Z, a-z, 0-9, and _ (underscore character)– First character must be a letter or underscore (no, _no 9no)– Usually only the first 32 characters are significant– There can be no embedded blanks (student no)– Identifiers are case sensitive (area, Area, AREA, ArEa)– Keywords cannot be used as identifiers



Reserved Words (Keywords) in C

auto break int longcase char register returnconst continue short signed

default do sizeof staticdouble else struct switchenum extern typedef unionfloat for unsigned voidgoto if volatile while



Naming Conventions• C programmers generally agree on the following

conventions for identifier:– Use meaningful identifiers– Separate words within identifiers with:

• underscores • capitalize each word

• Examples: – surfaceArea – SurfaceArea – Surface_Area



Variable declaration• Before using a variable, you must declare it

Data_Type Identifier;• int width; // width of rectangle• float area; // result of calculating area stored in it• char separator; // word separator

Data_Type Identifier = Initial_Value;• int width = 10; // width of rectangle• float area = 255; // result of calculating area stored in it• char seperator = ‘,’; // word separator

Data_Type Identifier, Identifier, Identifier ,….;• int width, length, temporary; • float radius, area = 0;



Variable declaration• When we declare a variable– Space is set aside in memory to hold a value of the

specified data type– That space is associated with the variable name– That space is associated with a unique address

• Visualization of the declaration– int width = 95; // get width form user– // &width is 22ff40– // *&width is 95– // sizeof width is 4

& *

address data

22ff40 95

22ff44



Data types• Minimal set of basic data types – primitive data types

• int • float • double • char • Void

• The size and range of these data types may vary among processor types and compilers



Data type qualifiers• Modify the behavior of data type to which they are applied:

– Size qualifiers: alter the size of the basic data types:• short: multiply by 0.5• long: multiply by 2• short can be applied to: int• long can be applied to: int and double

– Sign qualifiers: can hold both positive and negative numbers, or only positive numbers.:• signed: + and -• unsigned: +• they can be applied to : int and char



Data type size and rangeRange Size Example Qualifier Data type

-128 .. 127 0 .. 255-128 .. 127

888

signed char c; unsigned char c; char c;

signedunsigned char

signed (16): -32768 .. 32767

unsigned (16): 0 .. 65535

signed (32): -2147483648 .. 2147483647

unsigned (32): 0 .. 4294967295

161616 or 3216 or 3216 or 3216 163232323264646464

signed short i; signed short int i; unsigned int i; int i; signed int i; short i; short int i; long i; long int i; signed long i; signed long int i; long long i; long long int i; signed long long i; signed long long int i;

signedunsignedshortlong

int

+/- 3.4e +/- 38 (~7 digits) 64 float f; float

+/- 1.7e +/- 308 (~15 digits) 6480

double d; long double d; long double



Overflow and Underflow/* The # character indicate a pre-processor directive; it's an instruction to the compiler to make it do something The <> character tell C to look in the system area for the file stdio.h. If I had given the name #include "stdio.h" instead it would tell the compiler to look in the current directory/*#include <stdio.h> /* * Function main begins program execution* Semi-colon is statement terminator, so it is as a signal to the compiler for end of line*/int main() { /* The 2 curly brackets { }, are used to specify the limits of the program block */ char letter = 'A'; // char variable to show ASCII code short shortVariable = 32769; // short variable for test overflow // printf command display string on the monitor printf("current value of shortVariable is = %d\n", shortVariable); printf("current value of letter is = %d", letter); printf("current value of letter is = %c", letter); system("PAUSE"); // pause the execution to show press any key … return 0; // indicate that program ended successfully}

current value of shortVariable is = -32767current value of letter is = 65current value of letter is = A



Program Error• Compile-time or syntax– is caused when the compiler cannot recognize a

statement

• Run-time– E.g. division by zero

• Logical– E.g. Overflow and Underflow










Integer constant value• Base 10: 1 915 +8 -90• Base 8: 074 0123 084• Base 16: 0x1 0X5 0x7fab

• unsigned: 5000u 4U• long: 123456789l 56L• unsigned long: 536489ul• long long : 5361254865LL 25lL

• Example :– 0xABu 0123uL 017LL



floating-point constant value• A floating-point value contains a decimal point

– 33.5 0.0 -657.983 .2 6.

• For example, the value 150.4582 is represented in scientific notation as– 1.504582 X 102

• and is represented in exponential notation (by the computer) as– 1.504582E+02 – This notation indicates that 1.504582 is multiplied by 10 raised to

the second power (E+02)• The E stands for “exponent”



Char and string constant value• Char

char c;c = 'A'; // d = 65;

• Stringprintf("string is array of char!!!");printf("example of escape sequence is \n");



Constant• Constants provide a way to define a variable which cannot be

modified by any other part in the code – #define: without memory consume– const: memory consume

• #define Identifier constant_value – #define PI 3.14– #define ERROR "Disk error " – #define ERROR "multiline \ message"– #define ONE 1 #define TWO ONE + ONE



Constant• const [Data_Type] Identifier = constant_value;– const p = 3; // const int p = 3;– const p; p = 3.14; // compile error– const p = 3.14; // p = 3 because default is int– const float p = 3.14;










Operators• Arithmetic Operators

– unary operators • operators that require only one operand

– binary operators• operators that require two operands

• Assignment Operators• Equality and Relational Operators• Logical Operators• Bitwise Operators • Conditional Operator• Comma Operator• sizeof

Width * High

Operator

Operand



Arithmetic Operators• Unary Operator

C operation Operator Expression Explanation

Positive + a = +3;

Negative - b = -4;

Increment ++ i++; Equivalent to i = i + 1

Decrement - - i - -; Equivalent to i = i - 1



PRE / POST Increment• Consider this example:

• But if we have:

910

int width = 9;printf("%d\n", width++);printf("%d\n", width);

int width = 9;printf("%d\n", width);width++;printf("%d\n", width);

1010

int width = 9;printf("%d\n", ++width);printf("%d\n", width);

int width = 9;width++;printf("%d\n", width);printf("%d\n", width);



PRE / POST Incrementint R = 10;int count = 10;

++ Or -- Statement Equivalent Statements R count

R = count++;R = count;count = count + 1; 10 11

R = ++count;count = count + 1;R = count; 11 11

R = count--;R = count;count = count – 1; 10 9

R = --count;count = count – 1;R = count; 9 9



Arithmetic Operators• Binary Operators

C operation Operator ExpressionAddition + b = a + 3;Subtraction - b = a – 4;Multiplication * b = a * 3;Division / b = a / c;Modulus (integer) % b = a % c;



Division• The division of variables of type integer will always

produce a variable of type integer as the result

• Example int a = 7, b; float z; b = a / 2; z = a / 2.0; printf("b = %d, z = %f\n", b, z);

b = 3, z = 3.500000

Since b is declared as an integer, the result of a/2 is 3, not 3.5



Modulus• You could only use modulus (%) operation on integer

variables (int, long, char) z = a % 2.0; // error z = a % 0; // error

• Exampleint a = 7, b, c;b = a % 2;c = a / 2;printf("b = %d\n", b);printf("c = %d\n", c);

Modulus will result in the remainder of a/2.

- a/2

a%2

integral

remainder

7 2

6 3

1



Assignment Operators• lvalue = rvalue;

int i;float f;i = 2; // *&i = 2;2 = i; // error: invalid lvalue in assignmentf = 5.6; i = f; // i = 5;i = -5.9; // i = -5;



Assignment Operators• Assignment operators are used to combine the '=' operator

with one of the binary arithmetic or bitwise operators

• Example : – c = 9;

Operator Expression Equivalent Statement Results

+= c += 7; c = c + 7; c = 16

-= c -= 8; c = c – 8; c = 1

*= c *= 10; c = c * 10; c = 90

/= c /= 5; c = c / 5; c = 1

%= c %= 5; c = c % 5; c = 4

&= c &= 2 ; c = c & 2; c = 0

^= c ^= 2; c = c ^ 2; c = 11

|= c |= 2; c = c | 2; c = 11

<<= c <<= 2; c = c << 2; c = 36

>>= c >>= 2; c = c >> 2; c = 2



Precedence Rules• The rules specify which of the operators will

be evaluated first– For example: x = 3 * a - ++b%3;

Precedence Operator Associativity Level1 (highest) () left to right

2 unary right to left3 * / % left to right4 + - left to right

5 (lowest) = += -= *= /= %= right to leftc = b = d = 5;



Precedence Rules• how would this statement be evaluated?– : x = 3 * a - ++b % 3;– What is the value for X, for: a = 2, b = 4?

x = 3 * a - ++b % 3;x = 3 * a - 5 % 3;x = 3 * a - 5 % 3;x = 6 - 5 % 3;x = 6 – 2;x = 4;



Precedence Rules• If we intend to have a statement evaluated differently

from the way specified by the precedence rules, we need to specify it using parentheses ( )– x = 3 * a - ++b % 3;

• Consider having the following statement:– x = 3 * ((a - ++b)%3);– the expression inside a parentheses will be evaluated first

• The inner parentheses will be evaluated earlier compared to the outer parentheses



Precedence Rules• how would this statement be evaluated?– x = 3 * ((a - ++b)%3); – What is the value for X, for: a = 2, b = 4?

x = 3 * ((a - ++b) % 3);x = 3 * ((a - 5) % 3);x = 3 * ((-3) % 3);x = 3 * 0;x = 0;



Precedence Rules• how would this statement be evaluated?– x = 3 * ++a – b--%3;– What is the value for X, for: a = 2, b = 4?

x = 3 * ++a – b-- % 3;x = 3 * ++a – b-- % 3;x = 3 * ++a – 4 % 3;x = 3 * 3 – 4 % 3;x = 9 – 1;x = 8;

b = b -1 , b = 3;



Equality and Relational Operators• Equality Operators:

• Relational Operators:

Operator Example Meaning== x == y x is equal to y!= x != y x is not equal to y

Operator Example Meaning > x > y x is greater than y< x < y x is less than y>= x >= y x is greater than or equal to y<= x <= y x is less than or equal to y



Logical Operators• Logical operators are useful when we want to test multiple

conditions– AND– OR – NOT

• C has not bool data type, but:– 0: evaluate to false

• If(0) printf(" …");– other: evaluate to true

• If(1) printf(" …");• If(-13) printf(" …");



&& - Logical AND• All the conditions must be true for the whole

expression to be true– Example: if (a == 1 && b == 2 && c == 3)• means that the if statement is only true when a == 1

and b == 2 and c == 3 If (a = 5) …

e1 e2 Result = e1 && e2false false false false true false true false false true true true

e1 e2 Result = e1 && e20 0 00 1 01 0 01 1 1



|| - Logical OR• The truth of one condition is enough to make

the whole expression true• Example: if (a == 1 || b == 2|| c == 3)– means the if statement is true when

either one of a, b or c has the right value

e1 e2 Result = e1 || e2false false false false true truetrue false truetrue true true

e1 e2 Result = e1 || e20 0 00 1 11 0 11 1 1



! - Logical NOT• Reverse the meaning of a condition• Example: if (!(radius > 90))– Means if radius not bigger than 90.

e1 Result = !e1false truefalse truetrue false true false

e1 Result = !e10 10 11 01 0



Bitwise Operators • Apply to all kinds of int and char types:– signed and unsigned – char, short, int, long, long long

Operator Name Description& AND Result is 1 if both operand bits are 1| OR Result is 1 if either operand bit is 1^ XOR Result is 1 if operand bits are different~ Not (Ones Complement) Each bit is reversed

<< Left Shift Multiply by 2>> Right Shift Divide by 2



Bitwise Operators • Applicable for low level programming, e.g.:– Port manipulation– I/O programming

• Usually: – &: set OFF one bit– |: set ON one bit– ^: reverse one bit



XOR

e1 e2 Result = e1 ^ e20 0 00 1 11 0 11 1 0



Examples• A = 199;• B = 90;• c = a & b = 66; • c = a | b = 233;• c = a ^ b = 157;• c = ~a = 56• c = a << 2 = 28;• c = a >> 3 = 24;

1 1 0 0 0 1 1 1

0 1 0 0 0 0 1 0

1 1 0 1 1 1 1 1

1 0 0 1 1 1 0 1

0 0 1 1 1 0 0 0

0 0 0 1 1 1 0 0

0 0 0 1 1 0 0 0

0 1 0 1 1 0 1 0



Conditional Operator• The conditional operator (?:) is used to simplify an if/else

statement– Condition ? Expression1 : Expression2;

• The statement above is equivalent to:if (Condition) Expression1;else Expression2;

• Which are more readable?



Conditional Operator• Example:

if/else statement:

if (total > 12) grade = ‘P’; else grade = ‘F’;

conditional statement:

(total > 12) ? grade = ‘P’: grade = ‘F’; OR

grade =( total > 12) ? ‘P’: ‘F’;



Conditional Operator• Example:

if/else statement:if (total > 12) printf(“Passed!!\n”);else printf(“Failed!!\n”);

Conditional Statement:printf(“%s!!\n”, total > 12 ? “Passed”: “Failed”);



Comma Operator• (Expression1 ,Expression2,…);• Example:– int x, y, z;– z = (x = 2, y = x + 1);– printf("z = %d", z);

int x, y, z; x = 2; y = x + 1; z = y; printf("z = %d", z);



sizeof• The sizeof keyword returns the number of bytes of the given

expression or type– returns an unsigned integer result

• sizeof variable_Identifier;• sizeof (variable_Identifier);• sizeof (Data_Taype);

• Example:– int x; – printf("size of x = %d", sizeof x);– printf("size of long long = %d", sizeof(long long));– printf("size of x = %d", sizeof (x));



Type Casting• Explicit Type cast: carried out by programmer using casting

int k, i = 7;float f = 10.14;char c = 'B';k = (i + f) % 3; // errork = (int)(i + f) % 3;

• Implicit Type cast: carried out by compiler automatically f = 65.6; i = f; //f = (int)f;c = i; // c = (int)i;



Type Casting char c = 'A'; short s = 1; int i; float f; double d;

i = (c + s); (int) (char) (short) (short)

(int)

d = (c / i) + (f * d) + (f + i); (char) (int) (float) (double) (float) (int) int double float

double

double



Precedence RulesPrimary Expression Operators () [] . -> left-to-rightUnary Operators * & + - ! ~ ++expr --expr (typecast) sizeof right-to-left

Binary Operators

* / %

left-to-right

+ ->> <<< > <= >=== !=&^|&&||

Ternary Operator ?: right-to-leftAssignment Operators = += -= *= /= %= >>= <<= &= ^= |= right-to-leftPost increment expr++ expr-- -Comma , left-to-right



Good Programming Practices• Place each variable declaration on its own line with a descriptive

comment

• Place a comment before each logical chunk of code describing what it does

• Do not place a comment on the same line as code – with the exception of variable declarations

• Use spaces around all arithmetic and assignment operators

• Use blank lines to enhance readability



Good Programming Practices• AVOID: variable names starting with an underscore– often used by the operating system and easy to miss

• Place a blank line between the last variable declaration and the first executable statement of the program

• Indent the body of the program

• Use all uppercase for symbolic constants (used in #define preprocessor directives)– Examples:• #define PI 3.14159• #define AGE 52

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