C99的关键字

// auto

void function() {

    auto int localVar = 0; // localVar has automatic storage duration, typical for local variables.

}



// break

for(int i = 0; i < 10; i++) {

    if(i == 5) break; // Exits the loop when i equals 5.

}



// case, default, switch

int num = 2;

switch(num) {

    case 1: 

        // Code for case 1

        break;

    case 2: 

        // Code for case 2

        break;

    default: 

        // Code if no case matches

        break;

}



// char

char letter = 'A'; // Declares a character variable.



// const

const int MAX = 100; // MAX is a constant, its value cannot be changed.



// continue

for(int i = 0; i < 10; i++) {

    if(i % 2 == 0) continue; // Skips the rest of the loop body for even numbers.

    // Odd numbers code here

}



// do, while

int count = 0;

do {

    // Code to execute

    count++;

} while(count < 5); // Loops until count is less than 5.



// double

double pi = 3.14159; // Declares a double-precision floating-point variable.



// else, if

int a = 5;

if(a > 10) {

    // Code if condition is true

} else {

    // Code if condition is false

}



// enum

enum colors {red, green, blue};

enum colors shirt = red; // Assigns the first value of enum colors to shirt.



// float

float temperature = 36.6f; // Declares a single-precision floating-point variable.



// for

for(int i = 0; i < 10; i++) {

    // Loop code here

}



// goto

label:

    // Code to jump to

goto label; // Jumps to the label.



// int

int age = 30; // Declares an integer variable.



// long

long distance = 1234567890L; // Declares a long integer variable.



// register

register int fastVar = 5; // Suggests that fastVar should be stored in a register for faster access.



// return

int add(int x, int y) {

    return x + y; // Returns the sum of x and y.

}



// short

short height = 170; // Declares a short integer variable.



// signed

signed int temperature = -20; // Explicitly declares a signed integer.



// sizeof

int size = sizeof(int); // Gets the size of int type in bytes.



// static

void counter() {

    static int count = 0; // count retains its value between function calls.

    count++;

}



// struct

struct Person {

    char name[50];

    int age;

};

struct Person person1; // Declares a variable of type Person.



// typedef

typedef unsigned int uint;

uint counter = 100; // Uses uint as an alias for unsigned int.



// union

union Data {

    int i;

    float f;

    char str[20];

};

union Data data; // Declares a variable of type Data, which can hold an int, a float, or a char array.



// unsigned

unsigned int positive = 300; // Declares an unsigned integer, ensuring it's non-negative.



// void

void myFunction() {

    // A function that returns no value.

}



// volatile

volatile int shared = 0; // Tells the compiler that the value of shared can be changed unexpectedly.



// while

int i = 0;

while(i < 5) {

    // Code to execute while i is less than 5.

    i++;

}