Earn4Blog

Output:

1

//true because

a = 1//false because

b = 0

Ternaries may be nested, but take care as they are prone to error for beginners. The following code finds the highest of 3 numbers:

Now write the code for finding the smallest of 3 numbers.

We will now rewrite the four-function calculator using switch instead of else if as follows:

//program-3.11 To illustrate else if-a 4 function calculator

#include <iostream.h>

void main()

{

float a = 4.56f; //note f for float

float b = 8.67f;

char op = '+';

switch (op) //switch(var) begins...note parentheses

{

case '+': //if switch variable matches '+'

cout << (a + b);

break; //exit the switch block

case '-': //if switch variable matches '-'

cout << (a - b);

break; //exit the switch block

case '*': //if switch variable matches '*'

cout << (a * b);

break; //exit the switch block

case '/': //if switch variable matches '/'

cout << (a / b);

break; //exit the switch block

default: //if no match is found

cout << "Error";

} //close of switch block

} //end of main()

Rewrite the above using cin >> to read from keyboard the values of a, b, op.

The default case is usually but not necessarily the last one. If break is not used it will execute all subsequent cases following a successful match-find.

Although use of switch (value) is more convenient and elegant, it cannot be used if the determining variable is a non-integer or if there are more than one determining variables [e.g., if (a > 5 && b < 4)].

Now we rewrite the program using integer values instead of characters for addition, subtraction, multiplication, and division operations.

#include <iostream.h>

void main()

{

float a = 4.56f; //note f for float

float b = 8.67f;

int op = 2;

switch (op) //switch(var) begins...note parentheses

{

case 1: //if switch variable matches '+'

cout << (a + b);

break; //exit the switch block

case 2: //if switch variable matches '-'

cout << (a - b);

break; //exit the switch block

case 3: //if switch variable matches '*'

cout << (a * b);

break; //exit the switch block

case 4: //if switch variable matches '/'

cout << (a / b);

break; //exit the switch block

default: //if no match is found

cout << "Error";

} //close of switch block

} //end of main()

When a single instruction or a set of instructions is to be performed repeatedly, subject to some preset condition(s), it is called a loop or iteration.

: The syntax consists of initial value of a variable, its final (exit) value, and how the variable will be incremented or decremented.

//program-3.12 To illustrate a for loop

#include <iostream.h>

void main()

{

int num, count;

for(count = 1; count <= 10; count++) //no semi-colon

{ // braces to include block

num = count * 2; //body of loop

cout << num << ", ";

} //end of loop

} //end of main()

The parenthesis after for consists of 3 elements separated by semi-colons. Here, for example,

the first element is initialization of the variable count (count = 0;)

the second is the condition for the loop to continue (so long as count <= 10;)

the third is how the count changes (count++;)

Thus the minimum for a loop to be technically correct is for(… ;… ;)

When there are more than one variables they are comma separated thus:

As in case of if, braces are not needed if there is only a single statement under a loop.

What is the difference between the following code segments?

(i) for(a=0; a<4; a++)

cout << "Hello!"; // no braces or block

cout << "Thank you"; //not under loop

(ii) for(a=0; a<4;a++)

{

cout << "Hello! "; // block within braces

cout << "Thank you"; //all under loop

}

The first one prints "Hello!" many times, but "Thank you" only once. Only the first statement is under loop.

The second one prints both "Hello!" and "Thank you" repeatedly, as both form a block under the loop.

We print the odd and even numbers thus:

#include <iostream.h>

void main()

{

int i;

for (i = 1; i <= 10; i += 2) //i += 2 means i = i + 2

cout << i << '\t'; //a tab for a space

cout << endl; //new line

for (i = 2; i <= 10; i += 2)

cout << i << '\t';

cout << endl;

}

The following program prints the factorial of any positive integer (not zero).

//program-3.13 To illustrate a for loop--factorial

#include <iostream.h>

void main()

{

int prod = 1; //initialize

int num = 5; //(1)

int cnt; //declare variables

for(cnt = 1; cnt <= num; cnt++)

prod *= cnt; //only one statement under loop

cout <<"Factorial is " << prod;

}

Rewrite the above code replacing line (1) above with cin >> num;

: The loop continues while (or so long as) the condition stated in parentheses after while is true. We shall rewrite the above program using a while loop.

//program-3.14 To illustrate a while loop--factorial

#include <iostream.h>

void main()

{

int prod = 1, cnt = 1, num = 5; //initializations

while (cnt <= num) //no semi-colon

{ //braces for multiple statements

prod *= cnt;

cnt++; //increment of cnt inside body

} // end of while loop

cout << "Factorial is " << prod;

}

The increment could have been done along with the statement prod *= cnt; and the program would stand thus:

#include <iostream.h>

void main()

{

int prod = 1, cnt = 1, num = 5; //initializations

while (cnt <= num) //no semi-colon
prod *= cnt++; //post increment

cout << "Factorial is " << prod;

}

: The loop is introduced by the key word do, followed by opening brace which contains the block of statements; after the closing brace the while condition is specified. Thus the first iteration is unconditional, the stipulations are checked at the end of the block for continuation or exit.

We shall rewrite the factorial program using do while loop.

//program-3.15 Factorial using do - while loop

#include <iostream.h>

void main()

{

int prod = 1, cnt = 1, num = 5;

do //no condition for first iteration

{

prod *= cnt;

cnt++; //increment of cnt inside body

} while (cnt <= num); //condition at end of loop

//for 2nd and all

//subsequent iteration

cout <<"Factorial is " << prod;

}

Here also we could have incremented cnt along with the statement prod *= cnt; and written the code thus:

#include <iostream.h>

void main()

{

int prod = 1, cnt = 1, num = 5;

do //no condition for first iteration

prod *= cnt++;

while (cnt <= num);

/*condition at end of loop for 2nd and all subsequent iteration*/

cout <<"Factorial is " << prod;

}

We have shown that the same program may be written using a for loop, a while loop or a do while loop. However, the following principle will broadly guide us in the choice of the most convenient form of loop in a program:

(a) Use for loop when the number of iteration is known (e.g., find the sum of first ten even numbers or print a statement five times.

(b) Use while or do while loop when only the final exit condition is known, the condition may be numerical (e.g., print Fibonocci Series up to 100) or non-numeric (e.g., repeatedly ask a user whether he wants to continue, exit when he says ‘n’).

(c) A while loop checks the condition before entering the loop, it may not enter the loop at all if the condition is false at the outset. A do while loop checks the condition at the end of the first iteration, so it will execute it at least once.

For example to print the first ten terms of Fibonocci Series we would prefer for loop, but to print Fibonocci Series up to and not exceeding 100 a do while loop (or a while loop) would be used.

Fibonocci series consists of numbers starting with 1, 1 such that each subsequent term is the sum of the preceding two terms.

//program-3.16 - Fibonocci Series first 10 terms

//1 1 2 3 5 8 13 21 34 55

#include <iostream.h>

void main()

{

int num1 = 1; int num2 = 1; int num3;

cout << num1 << " " << num2 << " ";

for (int term = 3; term <=10; term++)

{

num3 = num1 + num2;

cout << num3 << " ";

num1 = num2; num2 = num3;

} //end of loop

}

Note the use of " " (space) between numbers.

//program-3.17 - Fibonocci Series below 100

#include <iostream.h>

void main()

{

int num1 = 1; int num2 = 1; int num3 = 2;

cout << num1 << " " << num2 << " ";

do

{

cout << num3 << " ";

num1 = num2; num2 = num3;

num3 = num1 + num2;

} while (num3 <= 100);

}