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==A negatively running for loop==

<source lang="csharp">using System;

class MainClass {
public static void Main() {
int x;

for(x = 100; x > -100; x -= 5)
Console.WriteLine(x);
}
}</source>
<pre class=codeResult>100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
-5
-10
-15
-20
-25
-30
-35
-40
-45
-50
-55
-60
-65
-70
-75
-80
-85
-90
-95</pre>

==Declare loop control variable inside the for==

<source lang="csharp">using System;

class MainClass {
public static void Main() {
int sum = 0;
int fact = 1;

for(int i = 1; i <= 5; i++) {
sum += i; // i is known throughout the loop
fact *= i;
}

// But, i is not known here.

Console.WriteLine("Sum is " + sum);
Console.WriteLine("Factorial is " + fact);
}
}</source>
<pre class=codeResult>Sum is 15
Factorial is 120</pre>

==Demonstrate a block of code inside if statement==

<source lang="csharp">using System;

class MainClass {
public static void Main() {
int i, j, d;

i = 5;
j = 10;

if(i != 0) {
Console.WriteLine("i does not equal zero");
d = j / i;
Console.WriteLine("j / i is " + d);
}
}
}</source>
<pre class=codeResult>i does not equal zero
j / i is 2</pre>

==for loop==

<p>You can repeatedly execute a sequence of code by creating a loop.</p>
<p>The general form of the for loop for repeating a single statement is</p>

<source lang="csharp">for(initialization; condition; iteration)
statement;</source>

==For loop with multiple expressions==

<source lang="csharp">using System;
class MainClass
{
static void Main()
{
const int count = 5;
for (int i = 0, j = 10; i < count; i++, j += 10)
{
Console.WriteLine("{0}, {1}", i, j);
}
}
}</source>
<pre class=codeResult>0, 10
1, 20
2, 30
3, 40
4, 50</pre>

==Loop condition can be any bool expression.==

<source lang="csharp">using System;

class MainClass {
public static void Main() {
int i, j;
bool done = false;

for(i=0, j=100; !done; i++, j--) {

if(i*i >= j) done = true;

Console.WriteLine("i, j: " + i + " " + j);
}

}
}</source>
<pre class=codeResult>i, j: 0 100
i, j: 1 99
i, j: 2 98
i, j: 3 97
i, j: 4 96
i, j: 5 95
i, j: 6 94
i, j: 7 93
i, j: 8 92
i, j: 9 91
i, j: 10 90</pre>

==Move "update" out of the for loop==

<source lang="csharp">using System;

class MainClass {
public static void Main() {
int i;

i = 0; // move initialization out of loop
for(; i < 10; ) {
Console.WriteLine("Pass #" + i);
i++; // increment loop control var
}

}
}</source>
<pre class=codeResult>Pass #0
Pass #1
Pass #2
Pass #3
Pass #4
Pass #5
Pass #6
Pass #7
Pass #8
Pass #9</pre>

==Nested for loop to calculate prime number==

<source lang="csharp">using System;

class MainClass {
public static void Main() {
int num;
int i;
int factor;
bool isprime;

for(num = 2; num < 20; num++) {
isprime = true;
factor = 0;

// see if num is evenly divisible
for(i=2; i <= num/2; i++) {
if((num % i) == 0) {
// num is evenly divisible -- not prime
isprime = false;
factor = i;
}
}

if(isprime)
Console.WriteLine(num + " is prime.");
else
Console.WriteLine("Largest factor of " + num +
" is " + factor);
}

}
}</source>
<pre class=codeResult>2 is prime.
3 is prime.
Largest factor of 4 is 2
5 is prime.
Largest factor of 6 is 3
7 is prime.
Largest factor of 8 is 4
Largest factor of 9 is 3
Largest factor of 10 is 5
11 is prime.
Largest factor of 12 is 6
13 is prime.
Largest factor of 14 is 7
Largest factor of 15 is 5
Largest factor of 16 is 8
17 is prime.
Largest factor of 18 is 9
19 is prime.</pre>

==Parts of the for can be empty.==

<source lang="csharp">using System;

class MainClass {
public static void Main() {
int i;

for(i = 0; i < 10; ) {
Console.WriteLine("Pass #" + i);
i++; // increment loop control var
}

}
}</source>
<pre class=codeResult>Pass #0
Pass #1
Pass #2
Pass #3
Pass #4
Pass #5
Pass #6
Pass #7
Pass #8
Pass #9</pre>

==The body of a loop can be empty==

<source lang="csharp">using System;

class MainClass {
public static void Main() {
int i;
int sum = 0;

// sum the numbers through 5
for(i = 1; i <= 5; sum += i++) ;

Console.WriteLine("Sum is " + sum);
}
}</source>
<pre class=codeResult>Sum is 15</pre>

==Use block inside for statement: Compute the sum and product of the numbers from 1 to 10==

<source lang="csharp">using System;

class MainClass {
public static void Main() {
int prod;
int sum;
int i;

sum = 0;
prod = 1;

for(i=1; i <= 10; i++) {
sum = sum + i;
prod = prod * i;
}
Console.WriteLine("Sum is " + sum);
Console.WriteLine("Product is " + prod);

}
}</source>
<pre class=codeResult>Sum is 55
Product is 3628800</pre>

==Use byte to control for loop==

<source lang="csharp">using System;

class MainClass {
public static void Main() {
byte x;
int sum;

sum = 0;
for(x = 1; x <= 100; x++)
sum = sum + x;

Console.WriteLine("Summation of 100 is " + sum);
}
}</source>
<pre class=codeResult>Summation of 100 is 5050</pre>

==Use commas in a for statement.==

<source lang="csharp">using System;

class MainClass {
public static void Main() {
int i, j;

for(i=0, j=10; i < j; i++, j--)
Console.WriteLine("i and j: " + i + " " + j);
}
}</source>
<pre class=codeResult>i and j: 0 10
i and j: 1 9
i and j: 2 8
i and j: 3 7
i and j: 4 6</pre>

==Use commas in a for statement to find the largest and smallest factor of a number==

<source lang="csharp">using System;

class MainClass {
public static void Main() {
int i, j;
int smallest, largest;
int num;

num = 100;

smallest = largest = 1;

for(i=2, j=num/2; (i <= num/2) & (j >= 2); i++, j--) {

if((smallest == 1) & ((num % i) == 0))
smallest = i;

if((largest == 1) & ((num % j) == 0))
largest = j;

}

Console.WriteLine("Largest factor: " + largest);
Console.WriteLine("Smallest factor: " + smallest);
}
}</source>
<pre class=codeResult>Largest factor: 50
Smallest factor: 2</pre>

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в 15:31, 26 мая 2010

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