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此文章为学习C语言时的案例笔记，用于记录各种案例。由于是从其他地方迁移至此，格式稍有错误。
- 分支结构
if(){ ... }else{ ... } switch(){ case():...;break; default:...; }continue/break //for循环不能用continue
- 简单计算器
#include int main(void) { int value1, value2; char op; printf ("Type in an expression: "); scanf ("%d%c%d", &value1, &op, &value2); switch (op){ case '+': printf ("=%d\n", value1 + value2); break; case '-': printf ("=%d\n", value1 - value2); break; case '*': printf ("=%d\n", value1 * value2); break; case '/': if (value2 != 0) printf ("=%d\n", value1 / value2); else printf ("Divisor can not be 0!\n"); break; case '%': if (value2 != 0) printf ("=%d\n", value1 % value2); else printf ("Divisor can not be 0!\n"); break; default: printf ("Unknown operator\n"); break; } return 0; } - 字符类型
Char → %d
挨个读取字符 → getchar ()ch = getchar () putchar ()
- 第三章
- 格雷戈里求圆周率
#include int main (void) { int denominator, flag; double item, pi; flag = 1; denominator = 1; item = 1.0; pi = 0; while (fabs (item) >= eps) { pi = pi + item; flag = -flag; denominator = denominator + 2; item = flag * 1.0 / denominator; } pi = pi + item; pi = pi * 4; printf ("pi = %.4f\n" , pi); return 0; } - 统计学生成绩
# include int main (void) { int count, num; double score, total; num = 0; total = 0; count=0; printf ("Enter scores: \n"); scanf ("%lf", &score); /* 输入第1个数*/ while (score >= 0) { /* 输入负数，循环结束 */ total = total + score; num++; if (score < 60) { count++; } scanf ("%lf", &score); } if (num != 0) { printf("Average is %.2f\n", total/num); printf("Number of failures is %d\n", count); } else { printf("Average is 0\n"); } return 0; } - 统计位数
do while循环do{ ... }while(...);#include int main (void) { int count, number; printf ("Enter a number: "); scanf ("%d", &number) ; if (number < 0){ number = -number; } count = 0; do { number = number / 10; count ++; } while (number != 0); printf ("It contains %d digits.\n", count); return 0; } - 判断素数
int main (void) { int count, number; printf ("Enter a number: "); scanf ("%d", &number) ; if (number < 0){ number = -number; } count = 0; do { number = number / 10; count ++; } while (number != 0); printf ("It contains %d digits.\n", count); return 0; } - 函数
- 计算圆柱体积
# include double cylinder (double r, double h); /* 函数声明*/ int main( void ) { double height, radius, volume; printf ("Enter radius and height: "); scanf ("%lf%lf", &radius, &height); /* 调用函数，返回值赋给volume */ volume = cylinder (radius, height ); printf ("Volume = %.3f\n", volume); return 0; } double cylinder (double r, double h) { double result; result = 3.1415926535*r*r; } -
double a1, a2, a3, a4, a5, a6, a7,s; double area(double x, double y, double z); printf("Please input 7 side lengths in the order a1 to a7:\n"); scanf("%lf%lf%lf%lf%lf%lf%lf", &a1, &a2, &a3, &a4, &a5, &a6, &a7); s = area(a1, a5, a6) + area(a4, a6, a7) + area(a2, a3, a7); /* 调用3次area */ printf("The area of the Pentagon is %.2f\n", s) ; /* 使用海伦-秦九韶公式计算三角形面积的函数 */ double area(double x, double y, double z) /* 函数首部 */ { double p = (x + y + z) / 2; return sqrt(p * ( p - x ) * ( p - y ) * ( p - z )) ; } - 数组
- 定义数组时，对数组元素赋初值
//类型名 数组名[数组长度] = {初值表}; int a[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; ==> a[0]=1, a[1]=2, ...… a[9]=10 - 静态数组、动态数组的初始化
//静态存储的数组如果没有初始化，所有元素自动赋0 static int b[5]; //动态存储的数组如果没有初始化，所有元素为随机值 auto int c[5]; 等价于 int c[5]; example: static int b[5] = {1, 2, 3}; b[0] = 1, b[1] = 2, b[2] = 3, b[3] = 0, b[4] = 0 auto int fib[20] = {0, 1}; fib[0] = 0, fib[1] = 1, 其余元素不确定 - 定义数组
#include #define MAXN 10 int main (){ int a[MAXN]; ... return 0; } - 求最小值
min = a[0]; for (i=1,i<n,i++){ if (a[i] < min){ min = a[i]; } } - 二分法查找
low = 0; high = n - 1; /* 开始时查找区间为整个数组 */ while ( low <= high ) { /* 循环条件 */ mid = (low + high) / 2; /* 中间位置 */ if ( x == a[mid] ){ break; /* 查找成功，中止循环 */ }else if ( x < a[mid] ){ high = mid - 1; /* 新查找区间为前半段，high前移 */ }else{ low = mid + 1; /* 新查找区间为后半段，low后移 */ } } if ( low <= high ){ printf("Index is %d \n", mid); }else{ printf( "Not Found\n"); } - 二维矩阵找最大值
# define MAXM 6 # define MAXN 6 int a[MAXM][MAXN]; printf ("Enter m, n: "); scanf ("%d%d", &m, &n); printf("Enter %d integers: \n", m*n); for ( i = 0; i < m; i++ ){ for ( j = 0; j < n; j++ ){ scanf ("%d", &a[i][j]);} } row = col = 0; for ( i = 0; i < m; i++ ){ for ( j = 0; j < n; j++ ){ if ( a[i][j] > a[row][col] ){ row = i; col = j; }} } printf ( "max = a[%d][%d] = %d\n", row, col, a[row][col] ); - 矩阵
- 二维矩阵初始化
分行赋初值 int a[3][3] = { {1, 2, 3} {4, 5, 6} {7, 8, 9} }; static int b[4][3] = { {1, 2, 3}, { }, {4, 5} }; 或 int a[][3] = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9} }; static int b[][3] = { {1, 2, 3}, { }, {4, 5} }; 数组a 1 2 3 4 5 6 7 8 9 数组b 1 2 3 0 0 0 4 5 0 0 0 0j = 0 j = 1 j = 2 i = 0 a[0][0] a[0][1] a[0][2] i = 1 a[1][0] a[1][1] a[1][2] i = 2 a[2][0] a[2][1] a[2][2]
i<=j //上三角 i>=j //下三角 i==j //主对角线 i+j==n-1//副对角线
- 字符和字符串数组
//一维字符数组 char t[5] = { 'H', 'a', 'p', 'p', 'y' }; static char s[6] = { 'H', 'a', 'p', 'p', 'y' }; //字符串可以存放在一维字符数组中 static char s[6] = { 'H', 'a', 'p', 'p', 'y', '\0' }; //字符数组初始化：用字符串常量 static char s[6] = { "Happy" }; static char s[6] = "Happy"; //数组长度 ≥ 字符串的有效长度 + 1 - 统计数字字符个数
#define MAXLINE 80 char str[MAXLINE]; printf("Enter a string: "); i = 0; while ((str[i] = getchar()) != '\n') { i++; } str[i] = '\0'; /* 输入结束符＝>字符串结束符 */ count = 0; for (i = 0; str[i] != '\0'; i++) { if (str[i] <= '9' && str[i] >= '0') { count++; } } printf("count = %d\n", count); - 凯撒密码
//将明文中的所有字母都在字母表上向后偏移offset位后被替换成密文 //当偏移量offset是2时，表示所有的字母被向后移动 2 位后的字母替换 //所有的字母 A 将被替换成C，字母 B 将变为 D，…，字母 X 变成 Z，字母 Y 则变为 A，字母 Z 变为 B。 #define M 26 scanf("%d", &offset); if(offset >= M) offset = offset % M; /* 移位效果相当于取其余数 */ /* 加密 */ for(i = 0; str[i] != '\0'; i++){ if(str[i] >= 'A' && str[i] <= 'Z'){ if((str[i] - 'A' + offset) < M) { str[i] = str[i] + offset; }else{ /* 如果向后越界 */ str[i] = str[i] - (M - offset); /* 循环移位 */ } }else if(str[i] >= 'a' && str[i] <= 'z'){ if((str[i] - 'a' + offset) < M) { str[i] = str[i] + offset; }else{ str[i] = str[i] - (M - offset); } } } - 指针
int *p, a = 3; p = &a; //把 a 的地址赋给 p，即 p 指向 a
- 模拟开锁
#include int main(void) { int x = 5342; /* 变量x用于存放密码值5342 */ int *p = NULL; /* 定义整型指针变量p，NULL值为0，代表空指针 */ p = &x; /*将变量x的地址存储在p中 */ /* 通过变量名x输出密码值*/ printf("If I know the name of the variable, I can get it's value by name: %d\n ", x); /* 通过变量x的地址输出密码值 */ printf("If I know the address of the variable is: %x, then I also can get it's value by address: %d\n", p, *p); return 0; } - 字符串压缩
#include #define MAXLINE 80 void zip(char *p); int main(void) { char line[MAXLINE]; printf("Input the string: "); gets(line); zip(line); puts(line); return 0; } void zip(char *p) { char *q = p; int n; while (*p != '\0') { n = 1; while (*p == *(p + n)) { n++; } if (n >= 10) { *q++ = (n / 10) + '0'; *q++ = (n % 10) + '0'; } else if (n >= 2) { *q++ = n + '0'; } *q++ = *(p + n - 1); p = p + n; } *q = '\0'; } - 字符数组与字符指针
char sa[ ] = "This is a string";//字符数组 char *sp = "This is a string";//字符指针 strcpy (sa, "Hello"); sp = "Hello"; //sp 可以直接赋值 //sa = “Hello”; 非法 //数组名是常量，不能对它赋值
- gets/puts
#include int main() { char str[80]; scanf("%s", str); //遇回车或空格输入结束，并自动将输入的一串字符和 '\0' 送入数组中 printf("%s", str); printf("%s", "Hello"); return 0; }#include int main() { char str[80]; gets(str); //遇回车输入结束，自动将输入的一串字符和 '\0' 送入数组中 puts(str); puts("Hello"); return 0; } - 字符串的复制
static char str1[20]; static char str2[20] = "happy"; strcpy (str1, str2); //str1中 h a p p y \0 strcpy (str1, “world”); //str1中: w o r l d \0
- 字符串的连接
#include "stdio.h" #include "string.h" int main(void) { char str1[80], str2[20]; gets(str1); gets(str2); strcat(str1, str2); puts(str1); return 0; } - 字符串的比较
//规则：按字典序(ASCII码序) //如果 str1 和 str2 相等，返回 0； //如果 str1 大于 str2 ，返回一个正整数； //如果 str1 小于 str2 ，返回一个负整数；
# include # include int main (void) { int res; char s1[20], s2[20]; gets (s1); gets (s2); res = strcmp (s1, s2); printf(“%d\n”, res); return 0; } - 字符串长度统计
static char str[20] = "How are you?" strlen ("hello");//值是：5 strlen (str);//值是：12 - 求最小字符串长度
int main ( ) { int i, n; int x, min; scanf ("%d", &n); scanf ("%d", &x); min = x; for (i = 1; i < n; i++){ scanf ("%d", &x); if (x < min) min = x; } printf ("min is %d\n", min); return 0; }int main() { int i, n; char sx[80], smin[80]; scanf ("%d", &n); scanf("%s", sx); strcpy (smin,sx); for (i = 1; i < n; i++){ scanf ("%s", sx); if (strcmp (sx, smin)<0) strcpy (smin,sx); } printf ("min is %s\n", smin); return 0; } - 结构
//单独定义：先定义一个结构类型，再定义一个具有这种结构类型的变量 struct student { int num; /* 学号 */ char name[10]; /* 姓名 */ int computer, english, math; /* 三门课程成绩 */ double average; /* 个人平均成绩 */ }; - 递归
- 用递归函数实现求n！
#include double fact(int n); int main(void) { int n; scanf("%d", &n); printf("%f", fact(n)); return 0; } double fact(int n) /* 函数定义 */ { double result; if (n == 1 || n == 0) /* 递归出口 */ { result = 1; } else { result = n * fact(n - 1); } return result; } - 将数字倒序输出
void reverse(int num) { if (num <= 9) { printf("%d", num); /* 递归出口 */ } else { printf("%d", num % 10); reverse(num / 10); /* 递归调用 */ } } - 宏定义
#include #define MAX(a, b) a > b ? a: b #define SQR(x) x * x
- 易错
#define F(x) x - 2 #define D(x) x*F(x) int main ( ) { printf ("%d,%d", D(3), D(D(3))) ; return 0; } - 正解
D (3) = x*F(x) 先用x替换展开 = x*x-2 进一步对F(x)展开，这里不能加括号 = 3*3-2 = 7 最后把x=3代进去计算 D(D(3)) = D(x*x-2) 先对D(3)用x替换展开， = x*x-2* F(x*x-2) 拿展开后的参数对D进一步进行宏替换 = x*x-2* x*x-2-2 拿展开后的参数对F进一步进行宏替换 = 3*3-2*3*3-2-2 = -13 最后把x=3代进去计算 运行结果：7 -13
- 长度单位转换
#include #define Mile_to_meter 1609 /* 1英里=1609米 */ #define Foot_to_centimeter 30.48 /* 1英尺=30.48厘米 */ #define Inch_to_centimeter 2.54 /* 1英寸=2.54厘米 */ int main(void) { float foot, inch, mile; /* 定义英里，英尺，英寸变量 */ printf("Input mile,foot and inch:"); scanf("%f%f%f", &mile, &foot, &inch); printf("%f miles=%f meters\n", mile, mile * Mile_to_meter); /* 计算英里的米数 */ printf("%f feet=%f centimeters\n", foot, foot * Foot_to_centimeter); /* 计算英尺的厘米数 */ printf("%f inches=%f centimeters\n", inch, inch * Inch_to_centimeter); /* 计算英寸的厘米数 */ return 0; } - 文件操作
- 暂无
