当前课程知识点：C Programming > Chapter 5 Loop Structure > 5.5 Loop Structure Program example 2 > 5.5 Loop structure program example 2.mp4
大家好，我是云南大学信息学院丁海燕老师
欢迎走进C语言程序设计课堂
今天我们接着讲解循环结构程序举例2
【例5】编程序，输出以下图形
使用双重循环实现
思路：
一共有4 行，每行由空格和星号组成
空格数按行增加，星号按行减少
变量 i 控制输出行数， 从1变化到4
变量 j 控制输出每行的空格和星号：
j 从1变化到 i，每次输出一个空格
j 从1变化到9 -2*i，每次输出一个星号
算法如图所示：
外循环,变量 i 控制输出行数,从1变化到4
内循环,顺序执行下列三个语句，
for语句j 从1变化到 i，每次输出一个空格
for语j 从1变化到9 -2*i，每次输出一个星号
输出一个换行符
程序如下：
{ int i,j;
for (i=1; i<=4; i++)
{ for (j=1; j<=i; j++)
printf(" ");
for (j=1;j<=9-2*i;j++)
printf("*");
printf(" ");} }
练习.打印如下的简单图案.
下面来看【例6】百鸡百钱问题
问题描述：一百个铜钱买一百只鸡
其中公鸡一只5 钱、母鸡一只3 钱
小鸡一钱3 只,问有多少种买法？
问题分析：
题意要求输出所有可能的方法
这是典型的穷举法
首先引入三个整数变量chick,hen,cock 分别
代表小鸡、母鸡和公鸡购买数量。考虑到一百个铜钱
顶多能买20 只公鸡，因此，cock 的取值范围
必在0~20 之间；hen 的变化范围应为0~(100-cock*5)/3
且满足条件： cock+hen+chick=100
cock*5+hen*3+chick/3=100
采用循环嵌套可解决此问题
程序描述：
{ int cock,hen,chick,count=0;
for(cock=0;cock<20;cock++)
for(hen=0;hen<33;hen++)
{ chick = 100 - cock-hen;
if ( (chick % 3 ==0) && (cock*5+hen*3+chick/3)==100)
{ count++;
printf("No.%d: cock=%d hen=%d chick=%d "
程序运行结果如图所示
请自行完成以下练习
1.用一元人民币兑换成1分、2分和5分硬币
共有多少种不同的兑换方法
2.有30个人，其中有男人、女人和小孩
3.在一家饭馆里吃饭共花了50先令，每个男人各花3先令
每个女人各花2先令，每个小孩各花1先令
问男人、女人和小孩各有几人？
例7.求 的近似值
解题思路：
–求 近似值的方法很多，本题是一种
–其他方法：
每项的分子都是1
后一项的分母是前一项的分母加2
第1项的符号为正，从第2项起
每一项的符号与前一项的符号相反
找到这个规律后，就可以用循环来处理了。
例如前一项的值是 ，则可以推出下一项为.
后一项的符号与上一项符号相反
在每求出一项后，检查它的绝对值是否>=10的负六次方
如果是，则还需要继续求下一项，直到某一项的值＜=10的负六次方
则不必再求下一项了，算法的N-S结构图如下
程序如下：
{ int sign=1; double pi=0,n=1,term=1;
while(fabs(term)>=1e-6)
{ pi=pi+term;
n=n+2;
sign=-sign;
term=sign/n;
pi=pi*4;
printf("pi=%10.8f ",pi);
其中，fabs(term)是求绝对值的函数
输出pi=3.14159065 只保证前5位小数是准确的
如果想提高精度，把while(fabs(term)>=1e-6)
中的1e-6改为1e-8，则输出pi=3.14159263
例8. 译密码。为使电文保密，往往按一定规律
将其转换成密码，收报人再按约定的规律将其译回原文
例如，可以按以下规律将电文变成密码
将字母A变成字母E, a变成e,即变成
其后的第4个字母，W变成A, X变成B, Y变成C, Z变成D
字母按上述规律转换
非字母字符保持原状不变.如“China!”转换为Glmre!”
输入一行字符，要求输出其相应的密码
•解题思路：问题的关键有两个：
(1)决定哪些字符不需要改变，哪些字符需要改变
(2)如果需要改变，应改为哪个字符
–处理的方法是: 输入一个字符给字符变量c
先判定它是否为字母(包括大小写)，若不是字母
不改变c的值；若是字母，则还要检查它是否’W’
到’Z’的范围内(包括大小写字母)。如不在此范围内
则使变量c的值改变为其后第4个字母
如果在’W’到’Z’的范围内
则应将它转换为A～D(或a～d)之一的字母
其中，输入一个字符给字符变量c,
用c=getchar(); 语句实现。
先判定它是否字母(包括大小写)，语句为
if((c>='a' && c<='z') || (c>='A' && c<='Z'))
检查字符是否在’W’到’Z’的范围内(包括大小写字母)
用下列语句计算转换后的字符
if(c>='W' && c<='Z' || c>='w' && c<='z')
c=c+4-26;
else c=c+4;
问题的第2个关键是：
(2) 怎样使c改变为所指定的字母？
–办法是改变它的ASCII值
–例如字符变量c的原值是大写字母’A’
想使c的值改变为’E’，只需执行“c=c+4”即可
因为’A’的ASCII值为65，而’E’ 的ASCII值为69
二者相差4
程序如下：
char c;
c=getchar(); //输入第一个字符
while(c!=‘ ’)
{ if((c>=‘a’ && c<=‘z’) || (c>=‘A’ && c<=‘Z’))
{ if(c>='W' && c<='Z' || c>='w' && c<='z')
c=c-22;
else c=c+4; }
printf("%c",c);
c=getchar(); //输入下一个字符}
输入 China!，则输出Glmre!
可以进一步改进程序。把前后两个读入
字符的c=getchar()合并为一个
并且放在while语句的检查条件中
char c;
while((c=getchar())!=‘ ’)
{ if((c>=‘A’ && c<=‘Z’) || (c>=‘a’ && c<=‘z’))
{ c=c+4;
if(c>‘Z’ && c<=‘Z’+4 || c>‘z’)
c=c-26; }
printf("%c",c); }
好了，同学们
循环结构程序举例2我们就学习到这儿
下节课再见！
-1.1 The development and characteristics of C language
--1.The development and characteristics of C language .mp4
--1.1 Self test questions
-1.2 A simple C Language program
--1.2 A simple C Language program.mp4
--【Source program】 Example 1.1 output a line of text Hello, world! "
--【Source program】 Example 1.2 program composed of multiple functions, find the larger of two integers
--1.2 Self test questions
-1.3 Program, Programming Language and C Program Running Steps
--1.3 Program, Programming Language and C Program Running Steps.mp4
--Running steps of C source program in CodeBlocks
--1.3 Self test questions
-chapter 1 Self-Test
-2.1 The Concept and Description of Algorithms
--2.1 The Concept and Description of Algorithms.mp4
--2.1 Self test questions
-2.2 Examples of Simple Algorithms, Computational Thinking and Structured Programming
--2.2 Examples of Simple Algorithms, Computational Thinking and Structured Programming.mp4
--2.2 Self test questions
-Chapter 2 Self test questions
-3.1 Simple Structure and Identifier of C Language Program
--3.1 Simple Structure and Identifier of C Language Program.mp4
--【Source program】 Example 3.1 input two integers and output the sum of two numbers.
--【Source program】 Example 3.2 input two integers and output the average value.
--【Source program】 Example 3.3 output the value of the character variable.
--3.1 Self test questions
-3.2 Constants, Variables and Assignments
--3.2 Constants, Variables and Assignments.mp4
--3.2 Self test questions
-3.3 Arithmetic, assignment, increment and decrement operators
--3.3 Arithmetic, assignment, increment and decrement operators.mp4
--3.3 Self test questions
-3.4 Conditions, commas, addresses, byte operators, and mixed operations among various numerical data
--3.4 Conditions, commas, addresses, byte operators, and mixed operations among various numerical data
--【Source program】 example of sizeof
--3.4 Self test questions
-3.5 Input and Output Examples and Character Input and Output
--3.5 Input and Output Examples and Character Input and Output.mp4
--【Source program】 Example. Find the root of quadratic equation of one variable.
--【Source program】 Example 1. Successively output three characters of BOY.
--【Source program】Example 2. Input 3 characters of BOY from the keyboard and output them to the screen
--3.5 Self test questions
-3.6 Formatted output printf function
--3.6 Formatted output printf function.mp4
--【Source program】 Example 3.4 output of integer data.
--【Source program】 Example 3.5 real data output.
--【Source program】 Example 3.6 character data output.
--【Source program】 Example 3.7 uses %s to output a string.
--3.6 Self test questions
-3.7 Formatted input scanf function
--3.7 Formatted input scanf function.mp4
--【Source program】 Example 3.8 Input and output integer data
--【Source program】Example 3.9 Input and output single precision and double precision real data.
--【Source program】Example 3.10 input and output character data.
--【Source program】Example 3.11 input and output string.
--3.7 Self test questions
-3.8 Basic Data Types of C Language
--3.8 Basic Data Types of C Language.mp4
--3.8 Self test questions
-Chapter 3 Self test questions
-Operator and expression self test questions
-4.1 Relational operators, logical operators, and if statements
--4.1 Relational operators, logical operators, and if statements.mp4
--【source example】Example 4.1 Find the root of the quadratic equation of one variable.
--【Source program】Example 4.2 Input two real numbers and output them from small to large.
--4.1 Self test questions
-4.2 Switch Statement
--【Source program】Example 4.3 uses switch statement to implement simple menu program
--【Source program】Example 4.4 converts centesimal score into the corresponding grade system score.
--4.2 Self test questions
-4.3 Examples of Selection Structural Programs
--4.3 Examples of Selection Structural Programs.mp4
--【Source program】 Example 4.5 determines whether a year is a leap year.
--【Source program】 Example 4.6 find the solution of quadratic equation of one variable.
--【Source program】Example 4.7 calculate the transportation cost for the user.
--4.3 Self test questions
-Chapter 4 Self test questions
-5.1 While and Do-While Statement
--5.1 While and Do…while statement.mp4
--【Source program】example 5.1 Use while statement to find 1 + 2 + 3 + +100
--【Source program】example 5.2 using do while statement to find 1 + 2 + 3 + +100
--5.1 Self test questions
-5.2 For Statement
--【Source program】example 5.3 Use for loop to find 1 + 2 + 3 +100
--5.2 Self test questions
-5.3 Change the State of Loop Execution and Nested Loop
--5.3 Change the state of loop execution and nested loop .mp4
--【Source program】example 5.4 collecting charity donations
--【Source program】example 5.5 output a number between 100 and 200 that cannot be divided by 3.
--【Source program】multiplication table
--【Source program】example 5.6 Output the following 4*5 matrix.
--5.3 Self test questions
-5.4 Loop Structure Program example 1
--5.4 Loop structure program example 1.mp4
--5.4 Self test questions
-5.5 Loop Structure Program example 2
--5.5 Loop structure program example 2.mp4
--【Source program】example 5. Output the following figure.
--【Source program】example6. The problem of 100 chickens and 100 coins
--【Source program】example 7. Find the approximate value of PI
--5.5 Self test questions
-Chapter 5 Self test questions
-6.1 Definition, Reference and Initialization of One-Dimensional Arrays
--6.1 Definition, Reference of One-Dimensional Arrays.mp4
--6.1 Self test questions
-6.2 One-Dimensional Array Programming
--6.2 One-Dimensional Array Programming.mp4
--【Source program】example 1. Fibonacci sequence
--【Source program】example 2. Find the maximum value and the minimum value.
--【Source program】example 3 exchanging array elements in reverse order.
--【Source program】example 4. Bubble sorting.
--6.2 Self test questions
-6.3 Definition, Reference and Initialization of Two-Dimensional Arrays
--6.3 Definition, Reference of Two-Dimensional Arrays.mp4
--6.3 Self test questions
-6.4 Two-Dimensional Array Programming
--6.4 Two-Dimensional Array Programming.mp4
--【Source program】example 1. Get the average score of each subject.
--【Source program】Example 2. The elements of row and column of a 2D array are interchanged
--6.4 Self test questions
-6.5 Definition, initialization and input and output of character arrays
--6.5 Definition, initialization and input and output of character arrays .mp4
--【Source program】Example 6.6 Output a known string.
--【Source program】Example 6.7 Output a diamond.
--【Source program】Example 6.10 Sorting of strings.
--6.5 Self test questions
-6.6 String Processing Function
--6.6 String Processing Function.mp4
--6.6 Self test questions
-6.7 Character Array Programming
--6.7 Character Array Programming.mp4
--6.7 Self test questions
-Chapter 6 Self test questions
-7.1 Function Concept and How to Define and Call Functions
--7.1 Function Concept and How to Define and Call Functions.mp4
--7.1 Self test questions
-7.2 Data Transfer in Function Call, Call Procedure and Function Return Value
--7.2 Data Transfer in Function Call, Call Procedure and Function Return Value.mp4
--7.2 Self test questions
-7.3 Declarations of called functions and nested calls to functions
--7.3 Declarations of called functions and nested calls to functions .mp4
--【Source program】Example 7.4 use a function to find the sum of t
--7.3 Self test questions
-7.4 Recursive call to function
--7.4 Recursive call to function.mp4
--【Source program】Example 7.6. How old is the fifth student?
--【Source program】Example 7.7 Use recursion method to find n!
--7.4 Self test questions
-7.5 Array as function parameter (1)
--7.5 Array as function parameter (1).mp4
--【Source program】Example 7.10
--7.5 Self test questions
-7.6 Array as function parameter (2)
--7.6 Array as function parameter (2).mp4
--【Source program】Selection sorting.
--【Source program】Example 7.13 find the maximum of a 3×4 matrix.
--7.6 Self test questions
-7.7 Local and global variables, internal and external functions
--7.7 Local and global variables, internal and external functions.mp4
--【Source program】Example 7.14
--7.7 Self test questions
-7.8 The Survival Period of Variables and the Storage Mode of Local Variables
--7.8 The Survival Period of Variables and the Storage Mode of Local Variables.mp4
--【Source program】Example 7.17
--7.8 Self test questions
-7.9 Storage Categories of Global Variables
--7.9 Storage Categories of Global Variables.mp4
--7.9 Self test questions
-Chapter 7 Self test questions
-8.1 Pointer Concept, Definition and Reference of Pointer Variables
--8.1 Pointer Concept, Definition and Reference of Pointer Variables.mp4
--8.1 Self test questions
-8.2 Pointer variables as function parameters
--8.2 Pointer variables as function parameters.mp4
--【Source program】Example 8.3. Exchange two data with function call.
--8.2 Self test questions
-8.3 Pointer of array element, operation of pointer and reference of array element by pointer
--8.3 Pointer of array element, operation of pointer and reference of array element by pointer.mp4
--【Source program】Point to array elements with pointer variables.
--8.3 Self test questions
-8.4 Using Array Name as Function Parameter
--8.4 Using Array Name as Function Parameter.mp4
--【Source program】Store array elements in reverse order.
--8.4 Self test questions
-8.5 Reference to multidimensional arrays by pointers
--8.5 Reference to multidimensional arrays by pointers.mp4
--【Source program】Pointer variable pointing to one-dimensional array.
--8.5 Self test questions
-8.6 Referencing strings through pointers
--8.6 Referencing strings through pointers.mp4
--【Source program】Reference string by pointer.
--8.6 Self test questions
-8.7 Character pointer as function parameter
--8.7 Character pointer as function parameter.mp4
--【Source program】Character pointer as function parameter.
--8.7 Self test questions
-8.8 Pointer pointing to function
--8.8 Pointer pointing to function.mp4
--【Source program】Pointer variable pointing to the function.
--8.8 Self test questions
-8.9 Functions that return pointer values
--8.9 Functions that return pointer values.mp4
--【Source program】Intercept substring.
--8.9 Self test questions
-8.10 Pointer arrays and multiple pointers
--8.10 Pointer arrays and multiple pointers.mp4
--【Source program】Sorting of strings.
--8.10 Self test questions
-8.11 Dynamic memory allocation and pointer variables pointing to it
--8.11 Dynamic memory allocation and pointer variables pointing to it.mp4
--【Source program】Dynamic memory allocation.
--8.11 Self test questions
-Chapter 8 Self test questions
-9.1 Define and use structural variables
--9.1 Define and use structural variables.mp4
--【Source program】Structure variable
--9.1 Self test questions
-9.2 Using structure arrays
--9.2 Using structure arrays.mp4
--【Source program】Structure array
--9.2 Self test questions
-9.3 Structure pointer
--【Source program】Structure pointer
--9.3 Self test questions
-Chapter 9 Self test questions
-CodeBlocks Baidu online disk download address
-Final Exam
--final exam
