03-函数、数组及指针

int main() {
    int x, result;
    
    x = 5;
    // 可以很容易看出 该程序的目标是计算数字的平方
    result = square(x);
    printf("%d squared is %d\n", x, result);
    return 0;
}

return_type function_name(parameters); 

#include <stdio.h>

/* 声明 */
int square (int num);

int main() {
    int x, result;
    
    x = 5;
    result = square(x);
    printf("%d squared is %d\n", x, result);
    
    return 0;
} 

#include <stdio.h>

/* 函数声明 */
int square (int num);

int main() {
    int x, result;
  
    x = 5;
    result = square(x);
    printf("%d squared is %d\n", x, result);
    
    return 0;
}

/* 函数定义 */
int square (int num) {
    int y;

    y = num * num;

    return(y);
}

int triple (___ num) {
    int y;
    y = num * 3;
}

#include <stdio.h>

int sum_up(int x, int y);

int main() {
    int x, y, result;

    x = 3;
    y = 12;
    result = sum_up(x, y);
    printf("%d + %d = %d", x, y, result);

    return 0;
}

int sum_up(int x, int y) {
    x += y;
    return (x);
} 

3 + 12 = 15

void test( ___  a, ___b);

#include <stdio.h>

// 全局变量
int global1 = 0;

int main() {
    // 局部变量
    int local1, local2;

    local1 = 5;
    local2 = 10;
    global1 = local1 + local2;
    printf("%d \n", global1);  /* 15 */

    return 0;
}

#include <stdio.h>

void say_hello();

int main() {
    int i;

    for (i = 0; i < 5; i++) {
        say_hello();
    }

    return 0;
}

void say_hello() {
    // 静态变量
    static int num_calls = 1;

    printf("Hello number %d\n", num_calls);
    num_calls++;
}

Hello number 1
Hello number 2
Hello number 3
Hello number 4
Hello number 5

___ int var ___ 1;

2*factorial(1)
3*factorial(2)
4*factorial(3)
5*factorial(4)

2 * 1
3 * 2
4 * 6
5 * 24

int fact(int n) {
    if (n == 1) {
        ___ 1;
    }
    return n * ___ (n - 1);
}

int test_scores[25]; /* 数组大小 25 */ 

float prices[5] = {3.2, 6.55, 10.49, 1.25, 0.99}; 

float prices[5] = {3.2, 6.55}; 

___ x ___ 4 ___ = {1, 2, 3, 4};

int x[5] = {20, 45, 16, 18, 22}; 

0 => [20]
1 => [45]
2 => [16]
3 => [18]
4 => [22]

#include <stdio.h>

int main() {
    int x[5] = {20, 45, 16, 18, 22};
    printf("The second element is %d\n", x[1]); /* 45 */ 
    
    return 0;
}

#include <stdio.h>

int main() {
    int x[5] = {20, 45, 16, 18, 22};
    x[1] = 260;
    printf("The second element is %d\n", x[1]); /* 260 */
    
	return 0;
}

int x[5] = {20, 45, 16, 18, 22};
printf("%d", x[___]);

#include <stdio.h>

int main() {
    float purchases[3] = {10.99, 14.25, 90.50};
    float total = 0;
    int k;

    /* 遍历 purchases，并累加 */
    for (k = 0; k < 3; k++) {
        total += purchases[k];
    }

    printf("Purchases total is %6.2f\n", total);
    /* Output:  Purchases total is 115.74 */

    return 0;
}

#include <stdio.h>

int main() {
    int a[10];
    int k;
    
    for (k = 0; k < 10; k++) {
        a[k] = k * 10;
    } 

    for (k = 0; k < 10; k++) {
        printf("%d \n", a[k]);
    }
   
	return 0;
}

int arr[5] = {1, 2, 3, 4, 5};
___ (int x = 0; x < ___; x++) {
    printf("%d", arr[___]);
}

int arr[] = {1, 2, 3, 4, 5};
int length = sizeof(arr) / sizeof(arr[0]);

int a[2][3]; /*  2 x 3 的数组 */ 

int a[2][3] = {
    {3, 2, 6},
    {4, 5, 20}
}; 

int a[2][3] = { {3, 2, 6}, {4, 5, 20} }; 

int arr[2][5];

#include <stdio.h>

int main() {
    int a[2][3] = {
        {3, 2, 6},
        {4, 5, 20}
    };
    printf("Element 3 in row 2 is %d\n", a[1][2]); /* 20 */
    a[1][2] = 25;
    printf("Element 3 in row 2 is %d\n", a[1][2]); /* 25 */
   
	return 0;
}

#include <stdio.h>

int main() {
    int num;
    printf("Enter a number: ");

    scanf("%d", &num);

    printf("%d", num);
    
	return 0;
}

#include <stdio.h>

void test(int k);

int main() {
    int i = 0;

    printf("The address of i is %x\n", &i);
    test(i);
    printf("The address of i is %x\n", &i);
    test(i);

    return 0;
}

void test(int k) {
    printf("The address of k is %x\n", &k);
} 

The address of i is 6faaf328
The address of k is 6faaf2ec
The address of i is 6faaf328
The address of k is 6faaf2ec

int var = 42;
printf("%___", ___ var)

pointer_type *identifier

#include <stdio.h>

int main() {
    int j = 63;
    int *p = NULL;
    p = &j;

    printf("The address of j is %x\n", &j);
    printf("p contains address %x\n", p);
    printf("The value of j is %d\n", j);
    printf("p is pointing to the value %d\n", *p);
}

The address of j is 6ba8b32c
p contains address 6ba8b32c
The value of j is 63
p is pointing to the value 63

int var = 42;
int ___ ptr = ___ var;

#include <stdio.h>

int main() {
    int x = 5;
    int y;
    int *p = NULL;
    p = &x;

    y = *p + 2; /* y 被赋予 7 */
    y += *p;     /* y 被赋予 12 */
    *p = y;       /* x 被赋予 12 */
    (*p)++;      /* x 增加到 13 */

    printf("p 指向值 %d\n", *p);
    printf("x 指的值 %d\n", x);
}

#include <stdio.h>

int main() {
    int a[5] = {22, 33, 44, 55, 66};
    int *ptr = NULL;
    int i;

    ptr = a;
    for (i = 0; i < 5; i++) {
        printf("%d ", *(ptr + i));
    }
}

22 33 44 55 66 

int a[5] = {22, 33, 44, 55, 66};
int *ptr = a;
int res = *(ptr + 2);
printf("%d", res);

#include <stdio.h>

int main() {
    int a[5] = {22, 33, 44, 55, 66};
    int *ptr = NULL;
        
    ptr = a;  /* point to the first array element */
    printf("%d  %x\n", *ptr, ptr);  /* 22 */
    ptr++;
    printf("%d  %x\n", *ptr, ptr);  /* 33 */
    ptr += 3;
    printf("%d  %x\n", *ptr, ptr);  /* 66 */
    ptr--;
    printf("%d  %x\n", *ptr, ptr);  /* 55 */
    ptr -= 2;
    printf("%d  %x\n", *ptr, ptr);  /* 33 */ 
}

22  6fc3f310
33  6fc3f314
66  6fc3f320
55  6fc3f31c
33  6fc3f314

int arr[] = {1, 2, 3};
int* ptr = arr;
ptr __;
printf("%d", ___);

#include <stdio.h>

void swap(int *num1, int *num2);

int main() {
    int x = 25;
    int y = 100;

    printf("x is %d, y is %d\n", x, y);
    swap(&x, &y);
    printf("x is %d, y is %d\n", x, y);

    return 0;
}

void swap(int *num1, int *num2) {
    int temp;

    temp = *num1;
    *num1 = *num2;
    *num2 = temp;
}

x is 25, y is 100
x is 100, y is 25

#include <stdio.h>

void test(int *x) {
    *x += *x / 2;
}

int main() {
    int v = 8;
    test(&v);
    printf("%d", v);
}

#include <stdio.h>

int add_up(int *a, int num_elements);

int main() {
    int orders[5] = {100, 220, 37, 16, 98};

    printf("Total orders is %d\n", add_up(orders, 5));

    return 0;
}

int add_up(int *a, int num_elements) {
    int total = 0;
    int k;

    for (k = 0; k < num_elements; k++) {
        total += a[k];
    }

    return (total);
}

___ foo(int ___ arr);

#include <stdio.h>

int *get_evens();

int main() {
    int *a;
    int k;

    a = get_evens(); /* get first 5 even numbers */
    for (k = 0; k < 5; k++)
        printf("%d\n", a[k]);

    return 0;
}

int *get_evens() {
    static int nums[5];
    int k;
    int even = 0;

    for (k = 0; k < 5; k++) {
        nums[k] = even += 2;
    }

    return (nums);
}

int ___getArray();

___ my_func(int a, ___ b);

void print(int n) {
    if (n < 0) {
        ___;
    }
    printf("%d", n);
    ___ (n - 1);
}

int arr[] = {1, 2, 3, 4, 5};
___ (int x = 0; x < 5; x++) {
    printf("%d", ___ [x]);
}

int num = 42;
int ___ ptr = ___ num;
___ ptr *= 2;

void swap(___ a, int *b) {
    int temp = *a;
    *a = *b;
    ___ b = temp;
}

int *test() {
    static int x[4];
    for (int i = 0; i < 4; i++) {
        x[i] = i % 2;
    }
    return x;
}

int main() {
    int *arr = test();
    printf("%d", *(arr + 3));
}