Looping II
(for statement)
Outline
 for statement
 Nested loops
 Compound assignment operators
 Increment and decrement operators
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while Statement
for Statement
 Syntax:
while (loop repetition condition)
statement;
 E.g.
Intialising loop
control variable
i = 1;
while (i <= 10)
for (i = 1; i <= 10; i = i + 1)
Testing loop control
{
cout << “*”;
variable
cout << “*”;
Updating loop control
i = i + 1;
variable
}
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for Statement
 It is used for a counter controlled loop
 Syntax:
for (initializing expression;
loop repetition condition;
update expression)
statement;
 condition test precedes the execution of
the loop body
 loop body may not be executed at all
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An Old Exercise
 Problem
Analyse, design, and implement an algorithm
that calculates and outputs the following sum:
sum = 1 + 2 + 3 + ……. + n
up to any number (n) input by the user.
 Analysis

Input
n: upper limit

Output
sum: sum of series

Intermediate variables
i: the current iteration number
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#include <iostream>
using namespace std;
 Design
START
INPUT
n
void main ()
{
int n, i, sum;
cin >> n;
i=1
sum = 0
OUTPUT False
sum
i = 1;
sum = 0;
while (i <= n)
{
i <= n ?
True
STOP
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sum = sum + i;
i = i +1;
sum = sum + i
i=i+1
}
}
cout << “The sum is “<<sum;6
#include <iostream>
using namespace std;
void main()
{
int i, n, sum = 0;
cout << “Please enter a whole number:“ << endl;
cin >> n;
for (i=1; i <= n; i = i + 1)
sum = sum + i;
cout << “The summation is:“ << sum << endl;
}
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#include <iostream>
using namespace std;
void main()
{
int i, n, sum = 0;
cout << “Please enter a whole number:“ << endl;
cin >> n;
for (i=n; i >= 1; i = i – 1)
sum = sum + i;
cout << “The summation is:“ << sum << endl;
}
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Nested Loops
 As with if statements, loop statements can
be nested
 Each time outer loop is repeated, any
inner loop is restarted - loop control
components are reevaluated and all
required iterations are performed
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Nested Loops (cont’d)
Write a program fragment that uses nested
loops to produce the following graphics:
a)
**********
**********
**********
**********
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for (row = 0; row <= 3; row = row + 1)
{
for (col = 0; col <= 9; col = col +1)
cout << ‘*’;
cout << endl;
}
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Nested Loops (cont’d)
b)
*
**
***
****
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for (row = 0; row <= 3; row = row + 1)
{
for (col = 0; col <= row; col = col +1)
cout << ‘*’;
cout << endl;
}
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Nested Loops (cont’d)
c)
0123456789
0123456789
0123456789
0123456789
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for (row = 0; row <= 3; row = row + 1)
{
for (col = 0; col <= 9; col = col +1)
cout << col;
cout << endl;
}
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Nested Loops (cont’d)
d)
0
01
012
0123
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for (row = 0; row <= 3; row = row + 1)
{
for (col = 0; col <= row; col = col +1)
cout << col;
cout << endl;
}
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Compound Assignment
Operators
 General form of
compound/special
assignment operators
variable = variable op exp.;
 General form of
common operations
variable op= exp.;
 E.g.
totalPay = totalPay + pay;
product = product * item;
countEmp = countEmp+1;
time = time - 1;
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+= -=
 E.g.
*=
/=
%=
totalPay += pay;
product *= item;
countEmp += 1;
time -= 1;
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Listing 5.3
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Using a for statement in a counting
loop
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Listing 5.5
Converting Celsius to
Fahrenheit
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Listing 5.5
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Converting Celsius to Fahrenheit
(continued)
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Output - Celsius to Fahrenheit
Celsius
10
5
0
-5
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Fahrenheit
50.00
41.00
32.00
23.00
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Increment and Decrement
Operators
++
- E.g.:


++i (instead of i = i + 1)
--i (instead of i = i - 1)
 Applied to a single variable
 Side effect: a change in the value of a variable
(by one) as a result of carrying out an operation
 Often used to update loop control variable
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#include <iostream>
using namespace std;
void main()
{
int i, n, factorial = 1;
cout << “Please enter a whole number:“;
cin >> n;
i = 2;
while (i <= n)
{
factorial = factorial * i;
i++;
// instead of i= i + 1;
}
cout << “The factorial is:“ << factorial << endl;
}
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Listing 5.13
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Nested for loop program
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Listing 5.13
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Nested for loop program
(continued)
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Listing 5.14
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Displaying the multiplication
table
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Listing 5.14
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Displaying the multiplication table
(continued)
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Increment and Decrement
Operators (cont’d)
 Prefix operator

E.g.
m = 3;
n = ++m;
 Postfix operator

E.g.
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m = 3;
n = m++;
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Exercise
What is the output from the following C++ segment?
int x = 1;
while (x <= 10)
{
cout<<x <<endl;
x += ++x;
}
while (x <= 91)
{
cout<<x <<endl;
x += x++;
}
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Exercise (cont’d)
Solution:
1
4
10
22
45
91
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Next lecture we will continue
Looping control construct in C++
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