Program Control Statements

Program control statemens are statements that control a program's flow of execution.

if else

Selectively execute part of a program through the use of the conditional statement if and else.

int i = 3;

if(3 == i) i++; // this statement consumes a single line which is OK to do

if(4 == i)
	i++; // i equals 4 so this line will execute
else
	i--; // this line will no execute

if(5 == i)
{
	i++; // inside a code block (see page 1 of this guide)
}
else
	i--;

if statements can be within if statements. This is known as nesting.

for

The for loop has this syntax:

for(initialization; condition; iteration) statement;

double d = 0.0;

for(int i = 0; i < 10; i++) // i will go from 0 to 9 and then stops when it hits 10
	d += i * 1.25; // this executes 10 times

for(int i = 1; i <= 10; i++) // i will go from 1 to 10 and then stops when it hits 11
{
	d += i * 1.25; // this executes 10 times
}

for loops can be nested.

while

The while loop has this syntax:

while(condition) statement;

int x = 0;
char c = 'z';

while(c >= 'a')
{
	x += c--;
}

do while

The do while loop checks its condition at the end after it has executed its block. It has this syntax:

do { statement; } while(condition);

int x = 0;
char c = 'z';

do
{
	x += c--;
}
while(c >= 'a');

break

It is possible to immediate exit a loop using a break statement.

double d = 0.0;

for(int i = 0; i < 10; i++)
{
	d += i * 1.25;
	if(d >= 100.0)
		break; // exit the loop
}

continue

It is possible to force an early iteration of a loop using a continue statement.

double d = 0.0;

for(int i = 0; i < 10; i++)
{
	d += i * 1.25;
	continue; // continues to the i++ iteration
	i = 1000; // this code will never execute
}

foreach

The foreach loop is used to cycle through a collection like an array, but it is not limited to arrays. This code demonstrates cycling through all the values of an array.

int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

foreach(int n in numbers)
{
	// do something with n
}

switch

The switch is a multiway branch. Its value of the expression is successively tested against a chain of constants.

int i = 2;

switch(i)
{
case 0:
	i++;
	break;
case 1:
	i--;
	break;
case 2:
	i = 10; // this line will execute
	break;
default:
	i += 100;
	break;
}

switch(i) // i now equals 10
{
case 0:
	i++;
	break;
case 1:
	i--;
	break;
case 2:
	i = 10;
	break;
default:
	i += 100; // this line will execute
	break;
}

switch statements can be nested.

using

The using statement uses an object inside its code block and when the code block ends, the Dispose() method (of the System.IDisposable interface) is called. This means the code will not have to explicitly call Dispose(). This is an elegant way to close network connections and open files, for example.

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