在C中打印數組的隨機元素

Question

我編寫了一個程序，該程序具有M * N個元素，其中用戶輸入了變量M和N。 該程序將在M x N表中打印元素，並為每個元素分配隨機值。 當我嘗試編譯程序時，不斷彈出兩個錯誤。 第一條消息說在第12行中有一個隱含的函數“ PopulateRandom”聲明。第二條消息說在第25行中的“ int”之前有一個缺少的表達式。

#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

編譯器抱怨函數PopulateRandom的隱式聲明，因為您在聲明/定義它之前先調用它。 在PrintArray2D調用PopulateRandom之前，只需對其進行定義。 關於這一點，您可能會發現這很有趣。 第二個問題可能是由以下代碼行引起的：

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

如果要連接更多條件，則應使用邏輯和（&&） 或/和邏輯或（||）。

您使用此while循環的方式使該方法不合適。 while循環不是for循環，語法不同。

for循環語法：

for (init; condition; increment)

While循環語法：

while (cond1 && cond2 || cond3)

我可以看到的其他問題是：

• 切換大小寫：您應該輸入default ，以防萬一。 另外，您總是必須打破案件。 您沒有打破case 1 。

switch statement一般語法：

switch  (x)
{
      case 1 :
             break;

      case n :
              break;

      default:
              break;
}

• 在PopulateRandom ：

  int array[int M * int N]

  應該

  int array []

  要么

  int *array

Answer 2

在此功能

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];
}

變量row ， column和i未初始化

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

但是同樣地，它們在循環中被相應地使用

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

在這個表達陳述中

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

此外，在此語句中，尚未聲明的函數調用后綴表達式中使用了名稱PopulateRandom 。 此外，在此表達式array[M * N]中，嘗試訪問數組之外​​的內存。

目前尚不清楚此魔術數字4在此聲明中的含義

if(column == 4){
            ^^^

也完全不清楚帶有未初始化變量i return語句的含義是什么

return array[i];

此函數聲明

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];
}

是無效的。 你可以寫例如

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

同樣，不清楚return語句的目的

return array[i];

嘗試返回數組中不存在的元素。

在標簽case 1:的switch語句中case 1:您應該附加break語句。

可以通過以下方式編寫循環

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 );

函數本身可以按照下面的演示程序中所示編寫

#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;
}

程序輸出可能看起來像

  1   2   2 
  3   5   0 

Answer 3

這是我在這個論壇上的第一個答案。 對我的解釋或更正要保持溫柔。 祝你今天愉快 ！ （這只是簡單的評論編）

#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);
    }
}