北京大学计算概论课件第九讲 循环结构.ppt

About ACM/POJ Due Time : 13th NOV recommended 22th NOV the dead line Call for report: Last 5 problems Other interesting problems Report outline: send to TA Wang, hujf@ Better before: 8th NOV Extra extra-score will be awarded Truth table (advanced) A Advanced topic about logic operation 000 001 010 011 100 101 110 111 Is leap year:  y%4==0 (y%100!=0 || y%400==0) Objectives Introduction of Loop Structures Sentinel-controlled repetition Counter-controlled repetition Nested loop Case study Dropping ball Repetition (dropping ball) Introduction of Loop Structures —— what is loop structure loop structure: a set of statements running again and again and again… Each time of running or executing is also called an iteration or one pass through of the loop Introduction of Loop Structures —— the unconditional Loop Structure Introduction of Loop Structures —— Conditional Loop Structure Different types of loop structures Unconditional loop structure Group of instructions computer executes repeatedly Conditional loop structure Sentinel-controlled loop structure Used when number of repetitions not known Sentinel value indicates end of data or operation“ Counter-controlled loop structure Definite repetition: know how many times loop will execute Control variable used to count repetitions Sentinel-controlled loop structure ——The while Statement The general form of the while statement is while (expression) statement; Back to the start of a while statement to reevaluate the expression The following is a valid but infinite loop: while (count = 10) printf(%d ,count); POJ: 1004 Conditional control Repetition statements conditional expression and control The for(;;) statement The for statement combines all four elements for (initializing; testing; altering) { statements; } items in parentheses can be omitted however, the two semicolons must be present for ( ; count++ = 20;) is va