C语言 用户输入数组大小 C
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User input array size C
提问by Marcus Rogers
Write a program that asks the users to enter a value for array size “n” and fill up the array with n integers. Then reverse the array and print it on the screen. I'm using Visual Studio and have this so far: I am having a problem with "size" in "int arr1[size]". It says it must be a constant value.
编写一个程序，要求用户输入数组大小“n”的值，并用 n 个整数填充数组。然后反转阵列并将其打印在屏幕上。我正在使用 Visual Studio 并且到目前为止有这个：我在“int arr1[size]”中遇到“size”问题。它说它必须是一个常数值。
#include <stdio.h>
int main(void)
{
int size, i;
printf("Enter the size of the arrays:\n");
scanf("%d", &size);
int arr1[size];
printf("Enter the elements of the array:\n");
for (i = 0; i < size; i++) {
scanf_s("%d", arr1[size]);
}
printf("The current array is:\n %d", arr1[i]);
}
回答by Alexander - Reinstate Monica
You can't use static memory allocation to allocate an array with a dynamic size. You'll need to dynamically request memory to be allocated to your program, by the operating system, of whatever dynamic size the use asks for.
您不能使用静态内存分配来分配具有动态大小的数组。您需要动态请求由操作系统分配给您的程序的内存，无论用户要求的动态大小如何。
Here's an example to get started:
下面是一个入门示例：
#include <stdlib.h>
#include <stdio.h>
void printArray(int *array, int size) {
// Sample array: [1, 2, 3, 4, 5]
printf("["); // [
for (int i = 0; i < size - 1; i++) { // [1, 2, 3, 4,
printf("%i, ", array[i]);
}
if (size >= 1) printf("%i", array[size-1]); // [1, 2, 3, 4, 5
printf("]\n"); // [1, 2, 3, 4, 5]
}
int main(void) {
int count;
printf("Enter the size of the array:\n");
scanf("%d", &count);
// ask for enough memory to fit `count` elements,
// each having the size of an `int`
int *array = malloc(count * sizeof(*array));
if (!array) {
printf("There was a problem with malloc.");
exit(EXIT_FAILURE);
}
printf("Enter the elements of the array:\n");
for (int i = 0; i < count; i++) scanf("%d", &array[i]);
printArray(array, count);
//do stuff
free(array);
}
回答by Basile Starynkevitch
Some dialects of C have variable-length arrays(VLA), notably C99(and GCCaccepts them....)
C 的一些方言具有可变长度数组(VLA)，特别是C99（并且GCC接受它们......）
But your teacher probably wants you to understand C dynamic memory allocation, and you should also test when scanffails, so you might code:
但是你的老师可能想让你了解C 动态内存分配，并且你也应该测试 when scanffailed，所以你可能会编码：
int main(void) {
int size, i;
printf("Enter the size of the arrays:\n");
if (scanf("%d", &size)<1) {
perror("scan size");
exit(EXIT_FAILURE);
};
Actually, you'll better test against the case of sizebeing negative! I leave that up to you.
实际上，您最好针对size阴性的情况进行测试！我把这留给你。
int *arr1 = calloc(size, sizeof(int));
if (arr1==NULL) {
perror("calloc arr1");
exit(EXIT_FAILURE);
}
You always need to handle failure of callocor malloc
您总是需要处理calloc或malloc
printf("Enter the elements of the array:\n");
for (i = 0; i < size; i++) {
if(scanf("%d", &arr1[size])<1) {
perror("scanf arr1[size]");
exit(EXIT_FAILURE);
}
}
scanf_sisonly existing in C11, and on a C11 compliant implementation you could use VLAs
scanf_s是只存在于C11，并在C11兼容的实现，你可以使用VLA小号
I leave the rest up to you. You want to code a forloop to print every element of the array.
我把剩下的留给你。您想编写一个for循环来打印数组的每个元素。
Of course you should call freeappropriately(and I am leaving that to you). Otherwise, you have a memory leak. Some systems have valgrindto help hunting them. Don't forget to compile with all warnings & debug info (with GCCuse gcc -Wall -g) then use the debugger(e.g. gdb).
当然，你应该free适当地打电话（我把它留给你）。否则，您将发生内存泄漏。一些系统有valgrind来帮助寻找它们。不要忘了所有警告和调试信息（与编译GCC使用gcc -Wall -g），然后使用调试器（如gdb）。
Don't forget that a programming language is a specification(written in some document), not a software. You may want to glance into n1570. And you need to understand what undefined behaviormeans.
回答by Tanmay Patil
In C , arrays can not be defined with user defined size in this fashion .
在 C 中，不能以这种方式用用户定义的大小定义数组。
Incorrect way :
不正确的方式：
int size, i;
printf("Enter the size of the arrays:\n");
scanf("%d", &size);
int arr1[size];
Correct way :
正确方法：
int size ;
int *arr1 ;
printf("Enter the size of the arrays:\n");
scanf("%d", &size);
arr1 = (int *) malloc(sizeof(int) * size);
