#include <stdio.h>

int main(void)
{
    char c = 'A';
    short s = 100;
    int i = 42;
    long l = 100000L;
    long long ll = 9876543210LL;

    float f = 3.14f;
    double d = 3.141592653589793;
    long double ld = 3.141592653589793238L;

    printf("char:        '%c' = %d, size = %zu\n", c, c, sizeof(char));
    printf("short:       %hd,       size = %zu\n", s, sizeof(short));
    printf("int:         %d,        size = %zu\n", i, sizeof(int));
    printf("long:        %ldL,      size = %zu\n", l, sizeof(long));
    printf("long long:   %lldLL,    size = %zu\n", ll, sizeof(long long));
    printf("float:       %f,        size = %zu\n", f, sizeof(float));
    printf("double:      %lf,       size = %zu\n", d, sizeof(double));
    printf("long double: %LfL,      size = %zu\n", ld, sizeof(long double));

    return 0;
}

gcc -Wall -std=c17 -o types types.c && ./types

#include <stdio.h>

int main(void)
{
    printf("sizeof(char)        = %zu\n", sizeof(char));
    printf("sizeof(int)         = %zu\n", sizeof(int));
    printf("sizeof(long)        = %zu\n", sizeof(long));
    printf("sizeof(long long)   = %zu\n", sizeof(long long));
    printf("sizeof(float)       = %zu\n", sizeof(float));
    printf("sizeof(double)      = %zu\n", sizeof(double));
    printf("sizeof(void *)      = %zu\n", sizeof(void *));

    int arr[10];
    printf("sizeof(arr)         = %zu\n", sizeof(arr));        // 10 * sizeof(int)
    printf("sizeof(arr)/sizeof(arr[0]) = %zu\n", sizeof(arr) / sizeof(arr[0])); // 元素个数

    return 0;
}

#include <stdio.h>

int main(void)
{
    signed int a = -10;      // 有符号，可为负
    unsigned int b = 10u;    // 无符号，仅非负

    printf("signed:   %d\n", a);
    printf("unsigned: %u\n", b);

    // 无符号与有符号混用的陷阱
    if (a < b) {
        printf("a < b\n");   // 实际上 -10 > 10（无符号比较）!
    } else {
        printf("a >= b\n");  // 这行会被执行
    }

    return 0;
}

int a = 5;
double b = 2.5;
double result = a + b;  // int 隐式提升为 double

#include <stdio.h>

int main(void)
{
    double pi = 3.14159;
    int truncated = (int)pi;      // 截断小数部分，结果为 3

    printf("pi = %f\n", pi);
    printf("(int)pi = %d\n", truncated);

    // 整数除法的陷阱
    int x = 7, y = 2;
    printf("7 / 2 = %d\n", x / y);             // 3（整数除法）
    printf("7 / 2 = %f\n", (double)x / y);     // 3.500000

    return 0;
}

#include <stdio.h>

int main(void)
{
    int i = 5;
    printf("i++ = %d, i = %d\n", i++, i);  // 先用后加: 5, 6
    i = 5;
    printf("++i = %d, i = %d\n", ++i, i);  // 先加后用: 6, 6
    return 0;
}

#include <stdio.h>

int main(void)
{
    int x = 0;

    // 短路求值：x != 0 为假，10/x 不会被执行
    if (x != 0 && 10 / x > 2) {
        printf("条件成立\n");
    } else {
        printf("x 为零或条件不成立，安全！\n");
    }

    return 0;
}

#include <stdio.h>

void print_binary(unsigned char val)
{
    for (int i = 7; i >= 0; i--) {
        printf("%d", (val >> i) & 1);
    }
}

int main(void)
{
    unsigned char a = 0xA5;  // 10100101
    unsigned char b = 0x0F;  // 00001111

    printf("a     = "); print_binary(a); printf("\n");
    printf("b     = "); print_binary(b); printf("\n");
    printf("a & b = "); print_binary(a & b); printf("\n");
    printf("a | b = "); print_binary(a | b); printf("\n");
    printf("a ^ b = "); print_binary(a ^ b); printf("\n");

    return 0;
}

#define FLAG_READ    (1 << 0)  // 0001
#define FLAG_WRITE   (1 << 1)  // 0010
#define FLAG_EXEC    (1 << 2)  // 0100

unsigned int perms = FLAG_READ | FLAG_WRITE;      // 设置读写权限
perms |= FLAG_EXEC;                                // 添加执行权限
perms &= ~FLAG_WRITE;                             // 移除写权限

if (perms & FLAG_READ) {
    printf("可读\n");
}

// 整型字面量
int decimal = 42;          // 十进制
int octal = 052;           // 八进制（前缀 0）
int hex = 0x2A;            // 十六进制（前缀 0x）
int binary = 0b101010;     // 二进制（C23，GCC 也支持）
long big = 1000000L;       // long 后缀
unsigned long long ull = 18446744073709551615ULL;

// 浮点字面量
float f = 3.14f;           // float 后缀
double d = 3.14;           // 默认 double
long double ld = 3.14L;    // long double 后缀
double sci = 1.5e10;       // 科学计数法

// 字符字面量
char c = 'A';
char newline = '\n';       // 转义字符
char hex_char = '\x41';    // 十六进制 ASCII

// 字符串字面量
const char *str = "Hello, World!";

// 转义字符表
// \n 换行  \t 制表符  \\ 反斜杠  \' 单引号  \" 双引号
// \0 空字符  \r 回车  \a 响铃  \b 退格

#include <stdio.h>

#define MAX_SIZE 100        // 宏常量（预处理期替换）
const int MIN_SIZE = 10;   // const 常量（编译期检查）

int main(void)
{
    const double PI = 3.14159265358979;
    // PI = 3.14;           // 错误！const 变量不可修改

    const int *p1 = &MIN_SIZE;    // 指向 const int 的指针
    int *const p2 = NULL;          // const 指针，指向 int
    const int *const p3 = &MIN_SIZE; // const 指针，指向 const int

    printf("MAX_SIZE = %d\n", MAX_SIZE);
    printf("MIN_SIZE = %d\n", MIN_SIZE);
    printf("PI = %f\n", PI);

    return 0;
}

#include <stdio.h>
#include <stdint.h>

typedef unsigned int uint;
typedef struct Point {
    double x;
    double y;
} Point;

typedef int (*MathFunc)(int, int);  // 函数指针类型别名

int add(int a, int b) { return a + b; }

int main(void)
{
    uint count = 42;
    Point p = {1.0, 2.0};
    MathFunc op = add;

    printf("count = %u\n", count);
    printf("point = (%.1f, %.1f)\n", p.x, p.y);
    printf("add(3, 5) = %d\n", op(3, 5));

    // 使用 stdint.h 中的定宽整型
    int32_t val = -100;
    uint32_t uval = 100;
    printf("int32_t: %d, uint32_t: %u\n", val, uval);

    return 0;
}

#include <stdio.h>

int main(void)
{
    // 大小写转换
    char lower = 'a';
    char upper = lower - 32;   // 'A'
    printf("%c -> %c\n", lower, upper);

    // 字符与数字互转
    char digit_char = '7';
    int digit = digit_char - '0';  // 7
    printf("'%c' -> %d\n", digit_char, digit);

    // 打印 ASCII 表
    for (int i = 32; i < 127; i++) {
        printf("%3d: '%c'  ", i, i);
        if ((i - 31) % 8 == 0) printf("\n");
    }

    return 0;
}

#include <stdio.h>
#include <limits.h>

int main(void)
{
    // 浮点精度问题
    double a = 0.1 + 0.2;
    printf("0.1 + 0.2 = %.20f\n", a);    // 不是精确的 0.3
    printf("0.1 + 0.2 == 0.3? %s\n", a == 0.3 ? "yes" : "no");

    // 整数溢出
    int max = INT_MAX;
    printf("INT_MAX = %d\n", max);
    // printf("%d\n", max + 1);  // 未定义行为！

    return 0;
}

#include <stdio.h>

int main(void)
{
    double celsius, fahrenheit;

    printf("请输入摄氏温度: ");
    if (scanf("%lf", &celsius) != 1) {
        fprintf(stderr, "输入错误！\n");
        return 1;
    }

    fahrenheit = celsius * 9.0 / 5.0 + 32.0;

    printf("%.1f°C = %.1f°F\n", celsius, fahrenheit);

    return 0;
}

gcc -Wall -std=c17 -o temp temp.c && echo "36.5" | ./temp