2/19/2016it 279, chung-chih li1 branching condition statement list 1 t f statement list 2 condition...

05/04/23 IT 279, Chung-Chih Li 1

Branching

Condition Statementlist 1

T

F

Statementlist 2

Condition Statementlist

T

F


The Syntax of if and if/else statements

if ( condition ) {

statement list;}

if ( condition ) {

statement list1;}else{

statement list2;}

Indentation indicates that the statements in the statement list are at the level next to the if/else statement.

Reserved words

A Boolean expression (logical expression). In C++, 0 is false, any non-zero values will be considered as true.

truefalse

A reserved word can’t be used as an identifier


#include <iostream>using namespace std;

void main(){

int a, b, c;

cin >> a >> b >> c;

if (a > b) {

}else{

}

cout << “ is the biggest”; }

if (a > c) cout << “a:” << a;

elsecout << “c:” << c;

if (b > c) cout << “b:” << b;

elsecout << “c:” << c;

max II


Operators

• Arithmetic operators:

+ - / * %• Relational operators:

== > < <= >= !=• Logical operators:

|| && !


Relational Operators

cout << (1 < 0) << endl; 0cout << (1 > 0) << endl; 1cout << (1 == 0) << endl; 0cout << (1 <= 0) << endl; 0cout << (1 >= 0) << endl; 1cout << ("1" > "0") << endl; 1cout << ("Yes" == "yes") << endl; 0cout << ("aab" > "aaa") << endl; 1cout << (2 < 3 < 4) << endl; cout << (4 > 3 > 2) << endl; cout << (4 > (3 > 2)) << endl; cout << (0 < 0.5 < 0.6) << endl;

== > < <= >= !=

1

10

0


Logical Operators

(1 || 0) ((18 <= x) && (x <= 50))

((18 <= x) || (x <= 50))

!(x < 5) is same as (x >= 5)

(((x % 2) == 0) && ((x % 3) == 0))

|| && !

Assume x = 10

true

true

true

false

false


De Morgan’s law

I am not a female student. I am not female or I am not a student.

I will not be in my office or in the lab. I will not be in my office and will not be in the lab.

!(A && B) is same as !A || !B

!(A || B) is same as !A && !B


Nested if/else statement

if ( condition 1 ) {

statement list;

}else{ statement list;}

Indentation indicates the level of statements.

if ( condition 2 ) {

statement list;}else{

statement list;};statement list;


Example of nested if/else statement

cout << "How many items do you want to buy? "; cin >> a; if (a == 1)

discount = 0.1; else {

if (a == 2) discount = 0.2; else { cout << "At most two items!!"; }

}

05/04/23 IT 279, Chung-Chih Li 10

Enumeration data type

int i,j;enum days {Mon, Tue, Wed, The, Fri, Sat, Sun};

enum days d1, d2=Wed;

....... d1=d2;

if (d1 < Sat) cout << d1 << “It is a week day”;else cout << d1 << “It is a weekend”;

05/04/23 IT 279, Chung-Chih Li 11

Enumeration data type II

enum days {Mon=1, Tue=2, Wed=3, The=4, Fri=5, Sat=6, Sun=7} d1;

.......

if (d1 < Sat) cout << d1 << “It is a week day”;else cout << d1 << “It is a weekend”;

enum days {Mon=5, Tue=4, Wed=3, The=2, Fri=1, Sat=0, Sun=0} d1;

.......

if (d1 != 0) cout << d1 << “It is a week day”;else cout << d1 << “It is a weekend”;

05/04/23 IT 279, Chung-Chih Li 12

Ambiguity in English

I saw the girl with a telescope.

I saw the girl with her boy friend.

05/04/23 IT 279, Chung-Chih Li 13

bool a_member, married;

// You don’t mean this:.....if (a_member)

if (married){ cout << “Input your spouse’s name:”; cin >> sname;}

elsecout << “Sorry, can’t get in!!”;

// A correct wayif (a_member){

if (married){

.....

}}else{

.....}

Ambiguity in C++

05/04/23 IT 279, Chung-Chih Li 14

Confusing nested if/else statement

bool weekend;enum days = {Mon, Tue, Wed, The, Fri, Sat, Sun};enum days d1=Mon, d2=Sun;

.......d1 = Sun;

if (d1 < Sat) if (d1 == Mon) cout << “Have a nice week!!\n”;else cout << “have a nice weekend\n”;

cout << “end\n”;

if (d1 < Sat){ if (d1 == Mon) cout << “Have a nice week!!\n”;}else cout << “have a nice weekend\n”;

cout << “end\n”;

05/04/23 IT 279, Chung-Chih Li 15

Cascaded if/else statements

if (condition_1) if (condition_2) if (condition_3) if (condition_4) if (condition_5) if (condition_6)

statement_1;else

statement_2;

if ( condition_1 && condition_2 &&

condition_3 && condition_4 && condition_5 &&

condition_6) statement_1;

else statement_2;

=

if (condition_1){ if (condition_2)

if (condition_3) if (condition_4)

if (condition_5) if (condition_6)

statement_1; else

statement_2;}

=

05/04/23 IT 279, Chung-Chih Li 16

Other forms of Nested if/else statements (Cascaded) I

if (condition_1) statement_1;

else if (condition_2) statement_2;











V.S.

05/04/23 IT 279, Chung-Chih Li 17

Other forms of Nested if/else statements (Cascaded) II

if (condition_1) if (condition_2) if (condition_3) if (condition_4) if (condition_5) if (condition_6)

statement_1;else

statement_2;

if ( condition_1 && condition_2 &&

condition_3 && condition_4 && condition_5 &&

condition_6) statement_1;

else statement_2;

=

05/04/23 IT 279, Chung-Chih Li 18

Switch vs. Cascaded if/else

if (i == 1) statement_1;

else if (i == 2) statement_2;





switch (i){

case 1: statement_1; break;





case 6: statement_6; break;}

05/04/23 IT 279, Chung-Chih Li 19

Example of switch

cout << "Input an integer as the day of the week:";cin >> i;

switch (i){ case 1 : cout << "\n Sunday";

break; case 2 : cout << "\n Monday"; break; case 3 : cout << "\n Tuesday"; break; case 4 : cout << "\n Wednesday"; break; case 5 : cout << "\n Thursday"; break; case 7 : cout << "\n Saturday"; break; case 6 : cout << "\n Friday"; break;

}

05/04/23 IT 279, Chung-Chih Li 20

breaks in a Switch statement

if (i == 1) statement_1;

else if (i == 2) {

statement_2; statement_3; }



switch (i){


case 2: statement_2;case 3: statement_3;

break;case 4: statement_4;

}

05/04/23 IT 279, Chung-Chih Li 21

LoopsBranching


T

F


T

F

05/04/23 IT 279, Chung-Chih Li 22

while


T

F

while (Condition){ Statement list}

05/04/23 IT 279, Chung-Chih Li 23

Example 1: while

string ans = “n”;

while (ans != “Y” && ans != “y”)

{cout << “Would you marry me?”;

cin >> ans;}

cout << “Great!!”;

Should I put ; here?

(ans != “Y” || ans != “y”)

Can I put ; here?

No!!

Up to you!!

05/04/23 IT 279, Chung-Chih Li 24

Example 2: while

int no_times;

cout << “How many times do you want to say?”;cin >> no_times;

while (no_times != 0){

cout << “Hello!” << endl;no_times--;

}

cout << “End!!” << endl;

Will there be any problem?

while (no_times > 0)

What if one inputs –1?

05/04/23 IT 279, Chung-Chih Li 25

Example 3: while

int a,b,sum;

cout << “This program will return the ”;cout << “summation of integers from a to b.\n\n”;cout << “Input two integers a and b:”;cin >> a >> b;

while (a <= b){

sum += a;a++;

}

cout << “The sum is ” << sum << endl;

sum = 0;

sum = sum + a;

Don’t forget to set sum = 0;

05/04/23 IT 279, Chung-Chih Li 26

Example 4: while

int a,b,sum=0;

cout << “This program will return the sum ”;cout << “of odd numbers between a and b.\n\n”;cout << “Input two integers a and b:”;cin >> a >> b;

while (a <= b){ if (a % 2) sum += a; a++;}

cout << “The answer is ” << sum << endl;

if (a % 2 == 0) a++;

while (a <= b){ sum += a; a += 2;}

3, 4, 5, 6 , 7

2, 3, 4, 5, 6 , 7

a b

05/04/23 IT 279, Chung-Chih Li 27

Example 5: while 3N+1 problem

long n,i=0;

cout << “Input an integer:”;cin >> n;

while (n > 1){ if (n % 2) n = 3*n+1; else

n /= 2; cout << ++i << “:” << n << endl;}

cout << “Done!!” << endl;

Will we always get out of a loop?

That is the question!! No one knows!

Input an integer:71:222:113:344:175:526:267:138:409:2010:1011:512:1613:814:415:216:1Done!!Press any key to continue

Input an integer:111:342:173:524:265:136:407:208:109:510:1611:812:413:214:1Done!!Press any key to continue

Input an integer:37591:112782:56393:169184:84595:253786:126897:38068..........83:1684:885:486:287:1Done!!Press any key to continue

05/04/23 IT 279, Chung-Chih Li 28

do-while

Condition

Statementlist

T

F

do {

Statement list} while (Condition);

string ans = “n”;while (ans != “Y”){

cout << “Would you marry me?”; cin >> ans;}


; is required

do{

cout << “Would you marry me?”; cin >> ans;} while (ans != “Y”);


05/04/23 IT 279, Chung-Chih Li 29

Example 1: do-while

int i;

....

do { cout << “Please input a number between ” << “10 and 20:”; cin >> i;} while (i < 10 || i > 20);

......

05/04/23 IT 279, Chung-Chih Li 30

Primality Test

A prime number is a positive integer that cannot be factorized, i.e., no numbers other that 1 and itself can divide it.

is 893 a prime?Is (893 % 2 == 0) ?Is (893 % 3 == 0) ?Is (893 % 4 == 0) ?Is (893 % 5 == 0) ?Is (893 % 6 == 0) ?

.

.

. Is (893 % 892 == 0) ?

We can write a loopto test these.

05/04/23 IT 279, Chung-Chih Li 31

Example: Silly Primality Test

long int p,r,i=2;

cout << “Input an positive integer:”;cin >> p;

cout << p << “ is “;

do{

r = p % i;i++;

} while (i < p && r != 0);

if (i == p) cout << “a prime number.”;else{ cout << “not a prime number.”; cout << “The least factor is ” << --i;}

05/04/23 IT 279, Chung-Chih Li 32

Break in a loop

do{

r = p % i;if (r == 0) break;i++;

} while (i < p);

The break statement in a loop will force theprogram to jump out of the loop immediately.

do {cout << “Would you marry me?”;cin >> ans;

cout << “Really?”cin >> ans;

} while (ans != “Y” && ans != “y”);cout << “Great!!”;

if (ans == “F” || and == “f”) break;

05/04/23 IT 279, Chung-Chih Li 33

Continue in a loop

The continue statement in a loop will force the program to check the loop condition immediately.

do {cout << “Would you marry me?”;cin >> ans;

if (and != “Y” && ans != “y”) continue;

cout << “Great?”

break;

} while (true);

....

05/04/23 IT 279, Chung-Chih Li 34

Euclid Algorithm#include <iostream>using namespace std;

void main(){int a,b;

cout << "Input two positive integers:";cin >> a >> b;

int r = a % b;

while (r){ a = b; b = r;

r = a % b;}cout << "The GCD is " << b << ".\n";

}

05/04/23 IT 279, Chung-Chih Li 35

Primality Test with while loop

#include <iostream>using namespace std;void main(){ bool is_prime=true;

int d=2,p;cout << "Input a positive integers:";cin >> p;

while (d <= p/2) {

if (p % d == 0) {

is_prime=false; break;

} d++;}if (is_prime) ...

}

Can we change to while (d < p/2) ?

05/04/23 IT 279, Chung-Chih Li 36

Primality Test with do-while loop

#include <iostream>using namespace std;void main(){ bool is_prime=true;


do { if (p % d == 0)

{ is_prime=false;

break; } d++;} while (d <= p/2);if (is_prime) ...

}

Can we change to while (d < p/2) ?

05/04/23 IT 279, Chung-Chih Li 37

Primality Test with do-while loop (a bit better)

void main(){ bool is_prime=true;


do { if ((p % d == 0) || (p % 2 == 0))

{ is_prime=false;

break; } d += 2;} while (d < p/2);

if (is_prime) ...}

05/04/23 IT 279, Chung-Chih Li 38

Primality Test with do-while loop (yet another improvement)

void main(){ bool is_prime=true;


if (p % 2 == 0} is_prime=false;

else do { if (p % d == 0)

{ is_prime=false;

break; } d += 2;} while (d < p/2);if (is_prime) ...

}

What if I forget else here?

05/04/23 IT 279, Chung-Chih Li 39

Definite Loop

• In programming a definite loop is more welcome.I.e., number of iterations isis known before the loop begins, at least the upper bound is known.

I.e., repeat the loop 100 times.

Precisely speaking, there is no definite loop in C++

05/04/23 IT 279, Chung-Chih Li 40

The general format for a for loop

for (Initialization_action; Condition; Condition_update){ statement_list;}

int n,f=1;

cin >> n;

for (i=2; i<=n; i++){ f *= i;} cout << “The factorial of ” << n << “ is ” << f << “.”;

1 2 3

Factorial of n is n(n-1)(n-2)...21

05/04/23 IT 279, Chung-Chih Li 41

Compare: for and while


int n,f=1;

cin >> n;

for (i=2; i<=n; i++){ f *= i;}

cout << “The factorial of ” << n << “ is ” << f << “.”;

i=2;while (i<=n){ f *= i; i++;}

1 2 3for (Initialization_action; Condition; Condition_update){ statement_list;}

05/04/23 IT 279, Chung-Chih Li 42

For Loop is not really a definite loop

int n,i;

n = 100;

for (i=1; i <= n; i++){ statement_list;}

int n,i;

n = 100;i = 1;

while (i <= n){ statement_list; i++;}

v.s.

05/04/23 IT 279, Chung-Chih Li 43

break and continue

The break statement in a for/while loop will force theprogram to jump out of the for/while loop immediately.

The continue statement in a for/while loop will force the program to update the loop condition and then check the condition immediately.


05/04/23 IT 279, Chung-Chih Li 44

Nested loops (loop in loop)

cin >> a >> b;

for (int i = 0; i < a; i++){

for (int j=0; j<b; j++){ cout << “*”;}cout << endl;

}

****************************************************

b

a

05/04/23 IT 279, Chung-Chih Li 45

Nested loops (2)

int a,b;

cin >> a >> b;

for (int i = 0; i < a; i++){

for (int j=0; j<b; j++){ if (j > i)

break; cout << “*”;}cout << endl;

}

**********

b

a

05/04/23 IT 279, Chung-Chih Li 46

Nested loops (3) **********

b

a

int a,b;

cin >> a >> b;

for (int i = 0; i < a; i++){ for (int j=0; j<b && j < i; j++)

{ cout << “*”;}cout << endl;

}

j <= i;

if (j > i) break;

05/04/23 IT 279, Chung-Chih Li 47

Nested loops (4)

int a,b;

cin >> a >> b;

for (int i = 0; i < a; i++){

for (int j=0; j<b; j++){ if (j < i)

cout << “ ”; else

cout << “*”;}cout << endl;

}

**********************************************

b

a

=

05/04/23 IT 279, Chung-Chih Li 48

Nested loops (5)

int a,i,j;cin >> a;

for (i = 0; i < a; i++) { for (j=0; j<a; j++) {

if (j < a-i) cout << " ";

else cout << "*"; }

for (j=0; j<a; j++) {if (j > i) break;cout << "*";

}

cout << endl;}

************************************

2/19/2016it 279, chung-chih li1 branching condition statement list 1 t f statement list 2 condition...

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