Repetition and Loop Statements Chapter 5 Repetition and Loop Statements 20061018 chap5

Repetition in Programs In most commercial software, you can repeat a process many times. When using an editor program, you can move the cursor to a program line and perform as many edit operations as you need to. Loop is a control structure that repeats a group of steps in a program. Three C loop control statements while for do-while 20061018 chap5

Flow Diagram of Loop Choice 20061018 chap5

Comparison of Loop Kinds 20061018 chap5

The while statement Counter-controlled loop (or counting loop) A loop whose required number of iterations can be determined before loop execution begins. The syntax while (loop repetition condition) statement; Loop repetition condition: the condition that controls loop repetition. Infinite loop: a loop that executes forever 20061018 chap5

Example count_emp = 0; /* no employees processed yet */ while (count_emp < 7) { /* test value of count_emp */ printf("Hours> "); scanf("%d", &hours); printf("Rate> "); scanf("%lf", &rate); pay = hours * rate; printf("Pay is $%6.2f\n", pay); count_emp = count_emp + 1; /* increment count_emp */ } printf("\nAll employees processed\n"); 20061018 chap5

Flowchart for a while Loop 20061018 chap5

Computing a Sum or a Product in a Loop Loops often accumulate a sum or a product by repeating an addition or multiplication operation. Accumulator A variable used to store a value being computed in increments during the execution of a loop. 20061018 chap5

Example 20061018 chap5

Compound Assignment Operators C provide special assignment operators variable op = expression; 20061018 chap5

The for Statement Three loop control components with the loop body. Initialization of the loop control variable, Test of the loop repetition condition, and Change (update) of the loop control variable. The for statement in C supplies a designed place for each of these three components . 20061018 chap5

Counting Loop by for Statement 20061018 chap5

for Statement 20061018 chap5

Increment and Decrement Operators The increment (i.e., ++) or decrement (i.e., --) operators are the frequently used operators which take only one operand. for(int i=0; i<100; i++) {…} for(int i=100; i>0; i--) {…} Side effect: the value of its operand is incremented/decremented by one. 20061018 chap5

Prefix and Postfix Increments The value of the expression in which the ++/-- operator is used depends on the position of the operator. 20061018 chap5

Example: Factorial Function 20061018 chap5

Inc. and Dec. Other Than 1 20061018 chap5

Conditional Loops In many programming situations, you will not be able to determine the exact number of loop repetitions before loop execution begins. Example: Monitor Gasoline Storage Tank (Fig. 5.9) 20061018 chap5

20061018 chap5

20061018 chap5

Loop Design Problem-Solving Questions for Loop Design What are the inputs? What are the outputs? Is there any repetition? Do I know in advance how many time steps will be repeated? How do I know how long to keep repeating the steps? Sentinel-Controlled Loops Endfile-Controlled Loops Infinite Loops on Faulty Data 20061018 chap5

Sentinel-Controlled Loops One way to do this is to instruct the user to enter a unique data value, called a sentinel value, after the last data item.(Fig. 5.10) 20061018 chap5

Endfile-Controlled Loops A data file is always terminated by an endfile character that can be detected by the scanf and fscanf functions. EOF stands for the endfile character. 20061018 chap5

Example of Endfile-Controlled Loops 20061018 chap5

Infinite Loops on Faulty Data Detect faulty data 20061018 chap5

Nested Loops Consist of an outer loop with one or more inner loops. (Fig. 5.13) 20061018 chap5

The do-while Statement When we know that a loop must execute at least one time. 20061018 chap5

Flag-Controlled Loops A flag is a variable used to represent whether or not a certain event has occurred. (Fig. 5.14) 20061018 chap5

20061018 chap5

Homework #5 Due: 2006/10/25 利用迴圈和 '*'可以畫出許多圖形 1.定義一個CENTER常數(#define CENTER 20)表示所有圖形的中心位置 2.實作出一個 function prototype 如下: void triangle(int n); 其作用是繪出 n 排星號的等腰三角形 若n為正時，則畫出三角形是正立的，如a. (n=4) 若n為負時，則畫出三角形是倒立的，如b. (n=-4) 3.主程式將輸入多個整數(最後以0結尾)，印出其對應的圖案 並判斷每個整數若不在-9 與 9 的範圍內則不予理會之 a. b. * ******* *** ***** ***** *** ******* * 20061018 chap5

Summary Repetition and Loop Statements while, for, and do-while Counter-Controller Loop Sentinel-Controller Loop Endfile-Controller Loop Input Validation Loop General Conditional Loop while, for, and do-while Compound Assignment Operators 20061018 chap5