nested loop

Saturday, December 16, 2006

“The whole of the development and operation of analysis are now capable of being executed by

machinery… As soon as an Analytical Engine exists, it will necessarily guide the

future course of science.”

- Charles Babbage (1792 - 1871)

Office hours today

Another way of writing this? if(num_credits < 0)

{ cout << "Come on, get real" << endl; } else if (num_credits < 12) { cout << "Part-time student" << endl; } else if (num_credits < 18) { cout << "Full-time student" << endl; } else { cout << "Glutton for punishment" << endl; }

Nested if statements The <statements> inside the braces can contain any valid C++

statements, including if statements!

// … some other code here

char answer;

if (withdrawal > balance)

{ cout << "Insufficient funds." << endl; cout << "Do you want to see your balance? "; cin >> answer; if (answer == 'y') cout<< "Your balance is "<<balance<< endl; } else { cout << "Here is your money." << endl; } cout << "Good bye." << endl;

Nested if statements if (x>y){if (x>z)statement1;if (x>p)statement2;elsestatement3;}elsestatement4;//bad style- no indentation (code with proper indentation on next

slide)

Nested if statements if (x>y){

if (x>z) statement1;

if (x>p) statement2;

else statement3;

}else

statement4;

/*else statement always refers to nearest if statement that is within same block as else and not already associated with another else*/

Nested if statements // what is wrong here? int main(){int x=10, y=2, z=12, p=13;if (x>y){

if (x>z) cout<<1<<endl;//statement1;

if (x>p) cout<<2<<endl;//statement2;

else cout<<3<<endl;//statement3;else

cout<<4<<endl;//statement4;}else

cout<<5<<endl;//statement5;

return 0;}

Nested if statements // what is wrong here? int main(){int x=10, y=2, z=12, p=13;if (x>y){

if (x>z) cout<<1<<endl;//statement1;

if (x>p) cout<<2<<endl;//statement2;

else cout<<3<<endl;//statement3;else //Error

cout<<4<<endl;//statement4;}else

cout<<5<<endl;//statement5;

return 0;}

Nested if statements // what is output here? int main(){

int x=10, y=2, z=12, p=13;if (x>y){

if (x>z){cout<<1<<endl;//statement1;if (x>p)

cout<<2<<endl;//statement2;else

cout<<3<<endl;//statement3;}else cout<<4<<endl;//statement4;

}else

cout<<5<<endl;//statement5;return 0;

}

Output is 4

SELF TEST // what is wrong here? int main(){

int x=10, y=2, z=12, p=13;if (x>y){

if (x>z) cout<<1<<endl;//statement1;

if (x>p) cout<<2<<endl;//statement2;

else cout<<3<<endl;//statement3;

cout<<4<<endl;//statement4; }else

cout<<5<<endl;//statement5;

return 0;}

SELF TEST // what is wrong here? int main(){

int x=10, y=2, z=12, p=13;if (x>y){

if (x>z) cout<<1<<endl;//statement1;

if (x>p) cout<<2<<endl;//statement2;

else cout<<3<<endl;//statement3;cout<<4<<endl;//statement4; /*this statement is not in the above else block, it will always be executed whenever we enter if(x>y) block. Try this code for x=10, y=2, z=3, p=13 and also for x=10, y=2, z=13, p=3 */

}else

cout<<5<<endl;//statement5;return 0;}

char alarm;int fuel_quantity, temperature, pressure;cout<<"Enter alarm fuel_quantity temperature pressure\n";cin>> alarm >> fuel_quantity >> temperature>> pressure;if (alarm=='y'){

if(fuel_quantity <10){cout<<"Add more fuel\n";

}else{

if (temperature >90){if (pressure >100)

cout<<"RED ALERT! Shut down motor\n";else

cout<<"Turn on pressure valve\n";}else {

cout<<"Check temperature again after 10 minutes\n";}

}

}else {

cout<<"No problem with motor\n";}

Loops of various sorts are used to repeat a set of statements some number of times.

Print numbers from 0 to 1000

int count_down=3;

while (count_down > 0)

{ cout << "Hello "; count_down -= 1;

}

int count_down=3;

while (count_down > 0)

{ cout << "Hello "; //count_down -= 1;

}

What happens now?

int x = 10;

while ( x > 0)

{ cout << x << endl; x = x – 3;

}

int x = 10;

while (x > 0)

{ cout << x << endl; x = x – 3;

}Output using the comparison x < 0 instead of x > 0?

What happens here?

int x = 1;

while (x != 12)

{ cout << x << endl;

x = x + 2;

}

Print the odd numbers less than 12

int x = 1;while (x != 12){ cout << x << endl;

x = x + 2;}How to fix it?

While loopsWhat's wrong with this?

int x = 10; while ( x > 0 ); { cout << x << endl; x--; }

While-loop and for-loop

int x = 1;

while (x < 12)

{

cout<<x<<endl;

x = x + 2;

}

The for loopfor (initialization; expression; increment){

//statements here}

Example: flowchart

int x = 1;

while (x < 12)

{

cout<<x<<endl;

x = x + 2;

}

int x = 1;

while (x < 12)

{

cout<<x<<endl;

x = x + 2;

}

for (x=1; x<12; x=x+2)

{

cout<<x<<endl;

}

int i ;for( i=0; i<10; ++i ){

cout << i << " ";}

int i;for( i=0; i<10; ++i ){

cout << i << " ";}

int i;for (i=0; i<10; i++){

cout <<i << " ";}

int x, n=100;for (x=0; x<n; x++){

x=x+1;}cout<<"x after end of loop is "<<x<<endl;

int x, n=100;for (x=0; x<n; x++){

x=x+1;}cout<<"x after end of loop is "<<x<<endl;

x is the smallest even number >= n

SELF TEST

int x, n=100;

for (x=0; x<n; x++){

cout<<x<<endl;

x=x+1;

}cout<<"x after end of loop is "<<x<<endl;

SELF TEST

int x, n=100;

for (x=0; x<n; x++){

x=x+1;

cout<<x<<endl;

}cout<<"x after end of loop is "<<x<<endl;

The For Loop

int i ;for( i=23; i>=30; ++i ){

cout << i << " ";}

for (i=13; i>=10; --i){

cout <<i <<" ";}

The For Loop

What is wrong here?int i, j, k ;for( i=0; i<10; i-- ){

cout<<i;}

for (i=0; i<10; ){

j=i+30;k=j+30;

}

Fibonacci numbers

F1=1

F2=2

Fn=Fn-1 + Fn-2

1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765 10946 17711 28657 …