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Objective-C Loops

2018年02月09日  | 移动技术网IT编程  | 我要评论

鬼殿遗祸,山东鲁能泰山队,皮亚松

　　There may be a situation, when you need to execute a block of code several number of times. In general, statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on.

　　Programming languages provide various control structures that allow for more complicated execution paths.

　　A loop statement allows us to execute a statement or group of statements multiple times and following is the general form of a loop statement in most of the programming languages:

　　Objective-C programming language provides the following types of loop to handle looping requirements. Click the following links to check their details.

Loop TypeDescription
while loop Repeats a statement or group of statements while a given condition is true. It tests the condition before executing the loop body.
for loop Execute a sequence of statements multiple times and abbreviates the code that manages the loop variable.
do...while loop Like a while statement, except that it tests the condition at the end of the loop body.
nested loops You can use one or more loops inside any another while, for or do..while loop.

Loop Control Statements:

　　Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed.

　　Objective-C supports the following control statements. Click the following links to check their details.

 

Loop TypeDescription
while loop Repeats a statement or group of statements while a given condition is true. It tests the condition before executing the loop body.
for loop Execute a sequence of statements multiple times and abbreviates the code that manages the loop variable.
do...while loop Like a while statement, except that it tests the condition at the end of the loop body.
nested loops You can use one or more loops inside any another while, for or do..while loop.

The Infinite Loop:

　　A loop becomes infinite loop if a condition never becomes false. The for loop is traditionally used for this purpose. Since none of the three expressions that form the for loop are required, you can make an endless loop by leaving the conditional expression empty.

#import <Foundation/Foundation.h>
 
int main ()
{
   for( ; ; )
   {
      NSLog(@"This loop will run forever.\n");
   }

   return 0;
}

　　When the conditional expression is absent, it is assumed to be true. You may have an initialization and increment expression, but Objective-C programmers more commonly use the for(;;) construct to signify an infinite loop.

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