在C中打印数组的随机元素

Question

我编写了一个包含 M*N 个元素的程序，其中变量 M 和 N 由用户输入。该程序打印 M x N 表中的元素，并为每个元素分配随机值。当我尝试编译程序时，不断弹出两个错误。第一条消息说在第 12 行有一个函数“PopulateRandom”的隐式声明。第二条消息说在第 25 行的“int”之前有一个缺少的表达式。

#include <stdio.h>
#include <stdlib.h>

// Prints elements of array in a M x N table
int PrintArray2D(int M, int N){
    int array[M*N], row, column, i;

    while(row <= M && column <= N){
    for(row = 0; row <= M; row++){
        for(column = 0; column <= N; column++){
            array[i] = PopulateRandom(array[M * N]);
            printf("%d", array[i]);
            if(column == 4){
                break;
            }
        }
        column = 0;
        printf("\n");
        }
    }
    return array[i];
}

//Assigns elements of the array "array" random values
int PopulateRandom(int array[int M * int N]){
    int i;

    while(i = 0; i < M*N; i++){
    array[i] = rand() % (M*N);
    }
    return array[i];
}

int main(void){
    int option, M, N;

    printf("If you would like to search ann array, enter 1 \n: ");
    printf("If you would like to exit, enter 0 \n: ");
    scanf("%d", &option);

    while(option != 0){
    switch(option){
        case 1: if(option == 1){
                printf("Enter two numbers M and N: ");                          
                scanf("%d %d", &M, &N);
                PrintArray2D(M, N);
        }
        case 0: if(option == 0){
            break;
        }
    }
    printf("If you would like to search ann array, enter 1 \n: ");
    printf("If you would like to exit, enter 0 \n: ");
    scanf("%d", &option);
    }
}

Answer 1

编译器抱怨函数 PopulateRandom 的隐式声明，因为您在之前声明/定义它之前调用它。在PrintArray2D 中调用它之前，只需定义PopulateRandom。 对此，您可能会发现 this 很有趣。 第二个问题可能是由这行代码引起的：

while(i = 0; i < M*N; i++)

如果您想连接更多条件，您应该使用逻辑与 (&&) 或/和 逻辑或 (||)。

您使用此 while 循环的方式不正确。 while 循环不是 for 循环，语法不同。

for循环语法：

for (init; condition; increment)

while循环语法：

while (cond1 && cond2 || cond3)

我能看到的其他问题是：

• 开关盒： 您应该发送default，以防万一。 此外，您总是必须破案。你没有破坏case 1。

switch statement 的一般语法：

switch  (x)
{
      case 1 :
             break;

      case n :
              break;

      default:
              break;
}

• 在PopulateRandom:

  int array[int M * int N]

  应该是

  int array []

  或

  int *array

Answer 2

在这个函数中

int PrintArray2D(int M, int N){
    int array[M*N], row, column, i;

    while(row <= M && column <= N){
    for(row = 0; row <= M; row++){
        for(column = 0; column <= N; column++){
            array[i] = PopulateRandom(array[M * N]);
            printf("%d", array[i]);
            if(column == 4){
                break;
            }
        }
        column = 0;
        printf("\n");
        }
    }
    return array[i];
}

变量row、column和i未初始化

int array[M*N], row, column, i;
                ^^^^^^^^^^^^^^

然而，它们在循环中相应地使用

while(row <= M && column <= N){

在这个表达式语句中

array[i] = PopulateRandom(array[M * N]);

此外，在此语句中，在尚未声明的函数调用后缀表达式中使用了名称 PopulateRandom。此外，在这个表达式array[M * N] 中，试图访问数组之外​​的内存。

不清楚这个神奇的数字 4 在这个语句中的含义

if(column == 4){
            ^^^

另外，这个带有未初始化变量i的return语句的含义是完全不清楚的

return array[i];

这个函数声明

int PopulateRandom(int array[int M * int N]){
    int i;

    while(i = 0; i < M*N; i++){
    array[i] = rand() % (M*N);
    }
    return array[i];
}

无效。你可以写例如

int PopulateRandom(int M, int N, int array[M * N]){
//...

同样不清楚return语句的目的

return array[i];

试图返回一个不存在的数组元素。

在标签 case 1: 的 switch 语句中，您应该附加 break 语句。

循环可以写成例如下面的方式

do
{
    printf("If you would like to search an array, enter 1 \n: ");
    //                                  ^^^ 
    printf("If you would like to exit, enter 0 \n: ");

    option = 0;
    scanf("%d", &option);

    switch( option )
    {
        case 1: 
        {
            printf("Enter two numbers M and N: ");                          
            scanf("%d %d", &M, &N);
            int a[M][N];
            PrintArray2D( M, N, a );
            break;
        }
    }
} while ( option != 0 );

函数本身可以写成如下演示程序所示

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

void PopulateRandom( int m, int n, int a[static const  m * n] )
{
    const int N = m * n;

    srand( ( unsigned int )time( NULL ) );

    for( int i = 0; i < N; i++ ) a[i] = rand() % N; 
}

void PrintArray2D( int m, int n, int a[static const m * n] )
{
    PopulateRandom( m, n, a );

    for ( int i = 0; i < m; i++ )
    {
        for ( int j = 0; j < n; j++ )
        {
            printf( "%3d ", a[i * n + j] );
        }
        printf( "\n" );
    }
}

int main(void) 
{
    int m = 2;
    int n = 3;
    int a[m * n];

    PrintArray2D( m, n, a );

    return 0;
}

程序输出可能看起来像

  1   2   2 
  3   5   0 

Answer 3

这是我在这个论坛的第一个答案。对我的解释或更正要温柔。祝你今天过得愉快 ！ （只是评论 prog 更简单）

#include <stdio.h>
#include <stdlib.h>
/*
-You need to use prototype or just set function "int PopulateRandom" before "int PrintArray2D"
-Try to change your way to process at this application, it's really so complicated.
-Try to use debug for understand what is going on your program.
*/

int PrintArray2D(int M, int N){
    int array[M*N], row, column, i; // Use "static int" for row, column and i for auto init at 0, or do it manually. 

    while(row <= M && column <= N){ // Like i have said in top, you use variable but they're not initialized
    for(row = 0; row <= M; row++){
        for(column = 0; column <= N; column++){
            array[i] = PopulateRandom(array[M * N]); // use directly "array[i] = (int) rand();" for change with random value
            printf("%d", array[i]); // you can directly print a random value, you save value, but when you leave this function, your array is destroy.
            if(column == 4){
                break;
            }
        }
        column = 0;
        printf("\n");
        }
    }
    return array[i]; // return is useless for your usage, becaus you don't catch return value in your main. (void PrintArray2D if no return)
}

/*
-Your function need other params : int array[], int M, int N (don't forget to send M and N when you call this function)
-You need to change your algo, because this function take M and N for change just ONE element of this array.
-This function is useless in this context, check comment in "PrintArray2D" for more informations
*/
int PopulateRandom(int array[int M * int N]){
    int i;

    while(i = 0; i < M*N; i++){ // It's a FOR and not WHILE
    array[i] = rand() % (M*N);
    }
    return array[i];
}

/*
-Duplicate code isn't good, you can use printf and scanf just one time, just after your while, and set option = 1 before.
-Donc use case, but just an if, because your condition in your while check the value.
*/
int main(void){
    int option, M, N;

    printf("If you would like to search ann array, enter 1 \n: ");
    printf("If you would like to exit, enter 0 \n: ");
    scanf("%d", &option);

    while(option != 0){
    switch(option){
        case 1: if(option == 1){
                printf("Enter two numbers M and N: ");                          
                scanf("%d %d", &M, &N);
                PrintArray2D(M, N);
        }
        case 0: if(option == 0){
            break;
        }
    }
    printf("If you would like to search ann array, enter 1 \n: ");
    printf("If you would like to exit, enter 0 \n: ");
    scanf("%d", &option);
    }
}