Question

我写了这个代码作为一个家庭作业问题，希望我通过使用指针算法-NOT SUBSCRIPTING-来访问数组元素来编写内部产品。但是，程序不允许我输入第三个元素后输入数字。为什么呢？

int inner_product(int *a, int *b, int size) 
{
  int sum = 0, i;

  for (i=0; i<size; i++) 
  {
    printf("enter value for first array: ");
    scanf("%d",*(a+i));
  }

  for (i=0; i<size; i++) 
  {
    printf("enter value for second array: ");
    scanf("%d",*(b+i));
  }

  for (i=0; i<size; i++) 
  sum += *(a+i) * *(b+i);

   return sum; 
}


int main()
{
    int n, *a, *b;
    printf("How many elements do you want to store?  ");
    scanf("%d",&n);
    a=(int *)malloc(n*sizeof(int));
    b=(int *)malloc(n*sizeof(int));

    printf("%d\n",inner_product(a,b,n));

    free(a);
    free(b);
}

Answer 1

在*(a+i)的来电中使用*(b+i)和scanf是不对的。他们需要(a+i)和(b+i)。

由于您将错误的参数传递给scanf，您正在遇到未定义的行为。

您需要提高编译器警告级别以在编译时检测这些错误。

当我使用gcc -Wall时，我收到以下警告：

soc.c: In function ‘inner_product’:
soc.c:11:5: warning: format ‘%d’ expects argument of type ‘int *’, but argument 2 has type ‘int’ [-Wformat=]
     scanf("%d",*(a+i));
     ^
soc.c:11:5: warning: format ‘%d’ expects argument of type ‘int *’, but argument 2 has type ‘int’ [-Wformat=]
soc.c:17:5: warning: format ‘%d’ expects argument of type ‘int *’, but argument 2 has type ‘int’ [-Wformat=]
     scanf("%d",*(b+i));
     ^
soc.c:17:5: warning: format ‘%d’ expects argument of type ‘int *’, but argument 2 has type ‘int’ [-Wformat=]

Answer 2

您可以修复警告。

$ gcc main.c 
main.c: In function ‘inner_product’:
main.c:11:15: warning: format ‘%d’ expects argument of type ‘int *’, but argument 2 has type ‘int’ [-Wformat=]
         scanf("%d",*(a+i));
               ^
main.c:17:15: warning: format ‘%d’ expects argument of type ‘int *’, but argument 2 has type ‘int’ [-Wformat=]
         scanf("%d",*(b+i));

如果我修正了警告，那么我可以输入4个元素：

$ ./a.out 
How many elements do you want to store?  4
enter value for first array: 2
enter value for first array: 3
enter value for first array: 4
enter value for first array: 5
enter value for second array: 3
enter value for second array: 4
enter value for second array: 5
enter value for second array: 6
68

我刚刚将调用从int更改为指针。

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

int inner_product(int *a, int *b, int size)
{
    int sum = 0, i;

    for (i=0; i<size; i++)
    {
        printf("enter value for first array: ");
        scanf("%d",(a+i));
    }

    for (i=0; i<size; i++)
    {
        printf("enter value for second array: ");
        scanf("%d",(b+i));
    }

    for (i=0; i<size; i++)
        sum += *(a+i) * *(b+i);

    return sum;
}


int main() {
    int n, *a, *b;
    printf("How many elements do you want to store?  ");
    scanf("%d", &n);
    a = (int *) malloc(n * sizeof(int));
    b = (int *) malloc(n * sizeof(int));

    printf("%d\n", inner_product(a, b, n));

    free(a);
    free(b);
}

C中的内部产品

2 个答案: