代码错误，用C编程

Question

我正在编写一个小程序作为练习：它假设添加向量。 我从 IDE 收到一条错误消息，指出：“错误：下标值既不是数组也不是指针也不是向量。” 当我通过一个 for 循环并让用户使用 scanf() 函数输入一些浮点类型的数据时，就会发生这种情况。我将在下面发布代码，以便您自己查看。

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

typedef struct
{
    float xcomp;
    float ycomp;

}vectors;

vectors initializeVector(vectors userVect, int length);


int main()
{


     /* This block determines the amount of vectors that will be added.
    It will then create an array of vector structs the size of the amount being added.
    Afterwards it will call a function that will grab the users data (vector information) and use
    to add the vectors in the array.*/


    int amount;
    printf("How many vectors would you like to add?\n");
    printf("AMOUNT: ");
    scanf("%d", &amount);
    vectors myvect[amount];


    initializeVector(myvect[amount],amount); //<-- This is a function call.
    return 0;

}


vectors initializeVector(vectors userVect, int length)
{
/* This function will go through the array of vectors and allow the user
to input the components of each vector in the array.*/

printf("Enter the 'X' and 'Y' components of your vector\n");
int i;
for(i=0; i<length;i++)
{
    printf("%d", i+1);
    printf(" vector:\n");
    printf("X: ");
    scanf("%f", userVect[i].xcomp); // This line brings up the error
    printf("\nY: ");
    scanf("%f", userVect[i].ycomp); //  this line brings up the error


    }



}

Answer 1

您需要使用 malloc 分配一个向量数组。

typedef struct
{
    float x;
    float y;
}vectors;

vectors initializeVector(vectors userVect[], int length);

int main()
{
    /* This block determines the amount of vectors that will be added.
    It will then create an array of vector structs the size of the amount being added.
    Afterwards it will call a function that will grab the users data (vector information) and use
    to add the vectors in the array.*/

    int amount;
    printf("How many vectors would you like to add?\n");
    printf("Count: ");
    scanf("%d", &amount);
    if(amount<1) { printf("error, need vector size %d > 0\n",amount); exit(1); }
    vectors *vectarray = malloc(sizeof(vectors)*amount); //allocate the vector for the given vector size
    if(!vectarray) { printf("error, cannot allocate vectorarray[%d]\n",amount); exit(2); }
    initializeVector(vectarray,amount); //<-- This is a function call.
    return 0;
}

然后您需要将该数组（作为指针）传递给初始化程序，并且您需要提供 x,y 组件的地址，而不仅仅是组件。

vectors initializeVector(vectors userVect[], int length) //pass an array
{
    /* This function will go through the array of vectors and allow the user
    to input the components of each vector in the array.*/

    printf("Enter the 'X' and 'Y' components of your vector\n");
    int i;
    for(i=0; i<length;i++)
    {
        printf("%d", i+1);
        printf(" vector:\n");
        printf("X: ");
        scanf("%f", &(userVect[i].x)); //scanf wants a pointer to the x component
        printf("\nY: ");
        scanf("%f", &(userVect[i].y)); //scanf wants a pointer to the y component
    }
}

Answer 2

您不能通过传递变量（数量）作为数组大小来静态分配数组。为此，您需要使用malloc 动态分配它。
此外，数组中的索引是从 0 开始的。这意味着您可以访问从 0 到 size-1 的元素。如果你通过 myvector[size] 你尝试在最后一个数组元素之后读取。