循环(程序设计)

1、2021-10-162/632021-10-163/63如何确定如何确定程序的输程序的输入和输出入和输出呢呢?Draw a flowchart for the following problem:读入读入5个整数，计算并显示它们的和个整数，计算并显示它们的和.Input : 5 个整数个整数n1, n2, n3, n4, n5 Output: n1, n2, n3, n4, n5的和的和Input example: 2 3 4 5 6Output example: 202021-10-164/63Input n1Input n2Input n3input n4input n5output su

2、msum n1+n2+n3+n4+n5n1Assume input example: 2 3 4 5 6n2n3n4n5sumend使用了使用了6个不同的变量个不同的变量start2021-10-165/631, 2, 3, 4, , 4, 3, 2, 12021-10-166/63counter 1, sum 0counter6sum sum + nfalsetruecounter+output suminput n1countersum01 6true2n0 + 2222 6true32 + 3533 6true45 + 4944 6true59 + 51455 6true614 + 62

3、066 6falsecounter-controlled 计数器每次增计数器每次增1使用了使用了3个变量个变量Assume input example: 2 3 4 5 6startend2021-10-167/63Step nStep xfalsetrue2021-10-168/63n当型循环当型循环Condition is tested first n计数控制计数控制Loop is controlled by a counternSyntax (initial value ; condition; update counter) statement;Or (initial value ;

4、condition; update counter) statement;statement; 复合语句复合语句compound statement被当作一条语句看待被当作一条语句看待循环变量控制循环次循环变量控制循环次数，不要在循环体内数，不要在循环体内改变这个变量的值改变这个变量的值2021-10-169/63i 0, sum 0i 5sumsum+ nfalsetruei+output suminput nint i, sum, n;sum = 0;for (i = 0; i 5; i+) scanf(“%d”, &n);sum = sum + n;printf(“%d”, sum);s

5、tartend2021-10-1610/63假假真真真真假假假假2021-10-1611/63 当型循环当型循环Condition is tested first 条件或计数控制条件或计数控制 Loop is controlled by condition or a counter 语法语法 Or2021-10-1612/63n直到型循环直到型循环Statements in the loop are executed first (at least once), and condition is tested lastn条件或计数控制条件或计数控制 Loop is controlled by

6、condition or a counter n语法语法2021-10-1613/632021-10-1614/63sum = 0的作用？的作用？ 2021-10-1615/632021-10-1616/63循环条件第一次就为假（如循环条件第一次就为假（如输入输入-1）时会怎样？）时会怎样？2021-10-1617/63真真假假假假假假 Testing Condition First2021-10-1618/63假假真真假假Testing condition last 2021-10-1619/632021-10-1620/632021-10-1621/632021-10-1622/63循环起

7、始条件循环起始条件循环变量增值循环变量增值循环结束条件循环结束条件2021-10-1623/632021-10-1624/632021-10-1625/63scanf()返回值为正确读入的数据项数返回值为正确读入的数据项数 清除输入缓冲区中的错误数据清除输入缓冲区中的错误数据 2021-10-1626/63标记值（标记值（Sentinel Value）2021-10-1627/632021-10-1628/632021-10-1629/63想一个想一个1100之间的数之间的数猜对猜对: right!猜错猜错: :wrong!并提示并提示大小大小2021-10-1630/632021-10-16

8、31/632021-10-1632/632021-10-1633/632021-10-1634/632021-10-1635/632021-10-1636/632021-10-1637/632021-10-1638/632021-10-1639/632021-10-1640/632021-10-1641/63每次单独计算每次单独计算累加项累加项2021-10-1642/63利用前项利用前项计算后项计算后项2021-10-1643/632021-10-1644/63?退出一层退出一层循环或循环或switch?中断此次中断此次循环，开始下一次循环，开始下一次2021-10-1645/63n?10P

9、lease enter n:10 n = 10Please enter n: -10 Program is over!-102021-10-1646/63n?10Please enter n:10 n = 10Please enter n: -10 Please enter n:20 n = 20Please enter n: -20 Please enter n:30 n = 30Program is over!-1020-20302021-10-1647/632021-10-1648/632021-10-1649/63“瞎猫碰死耗子瞎猫碰死耗子”2021-10-1650/63“死循环死循环”2021-10-1651/632021-10-1652/632021-10-1653/63标准库函数，标准库函数，作用是终止整作用是终止整个程序的执行，个程序的执行，强制返回操作强制返回操作系统系统 2021-10-1654/63结