为什么这个 C 程序不在 Microsoft Visual Studio 上运行？

Question

I am tried to run after building this without any warnings or errors in Visual Studio.

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

int e = 0;
int num = 0;
int a = 0;
int n = 0;
int c = 0;

static int factorial();

int factorial(int e){
  if (e == 0)
    return 1;
  else if (e == 1)
    return 1;
  else
  return e * factorial(e - 1);
}

int main() {
  int k = 0;
  int i = 0;
  int j = 0;
  int f = 0;
  int r = 0;

  printf_s(" Enter a number for length of string");  
  scanf_s("%d", &n);
  printf_s(" Enter a number for choice of string");
  scanf_s("%d", &k);
  f = factorial(n) / (factorial(n - 2) * 2);
  char **arr = (char **)malloc(n * sizeof(char *));
  
  for (i = 0; i < n; i++){
    arr[i] = (char*)malloc(f * sizeof(char));
  }

  for (i = 0; i < n; i++){
    for (j = 0; j < f; j++) {
      *(*(arr + i) + j) = '\0';
    }
  }

  for (i = 1; i < n; i++){
    num = 0;
    for (j = 0; j < i; j++){
      while (num <= n){
        if ((num == j) || (num == i))
          arr[r][num] = 'b';
        else
          arr[r][num] = 'a';
      }
    }
    r++;
  }

  for (i = 0; i < n; i++) {
    for    j = 0; j < f; j++) {
      printf_s("%c ", arr[j][i]);
    }
  }
}

The control goes out of control after taking the inputs. Whitespace characters, new line, any characters, strings or gibberish doesn't make any difference. I also have my doubts about my calling the factorial function like an expression.

Answer 1

I know this should be a comment but since I am lacking on reputation points, I can't comment. But from what I understand this code snippet:

'for (i = 0; i < n; i++) {
    for    j = 0; j < f; j++) {
      printf_s("%c ", arr[j][i]);
    }
  }
}'

has an error; there should be a opening bracket in the second for loop. How did you manage to run it in spite of a compilation error to get a run time error I don't know. I think you pasted an older version of your code. Apart from that I admit I don't even know about printf_s() function. and from what I ran on my system it is throwing a undefined reference to both printf_s() and scanf_s(). If its a built in function make sure you have included its header file. Apart from that in this code snippet:

for (i = 1; i < n; i++){
    num = 0;
    for (j = 0; j < i; j++){
      while (num <= n){
        if ((num == j) || (num == i))
          arr[r][num] = 'b';
        else
          arr[r][num] = 'a';
      }
    }
    r++;
  }

in the while loop num and n do not change so it is an infinite loop. I think that is the main reason for your error.

Answer 2

factorial() is ok, but there is no point in writing else after return

int factorial(int e)
{
    if (e == 0) return 1;
    if (e == 1) return 1;
    return e * factorial(e - 1);
};

sure you can also write a single if() using ||

Your prototype for factorial is missing the parameter as in int factorial(int);

A left '(' is missing at line 56, the for j = 0 as pointed by others

In this code

    for (i = 0; i < n; i++) {
    arr[i] = (char*)malloc(f * sizeof(char));
}

for (i = 0; i < n; i++) {
    for (j = 0; j < f; j++) {
        *(*(arr + i) + j) = '\0';
    }
}

You can initialize the strings in the first loop. No need to go again looping into them

Note that the safe version of scanf() expect a size parameter for each specifier of type %c %s or %[ ] (not the case here, you are using %d only).

Could you write a bit more on the logic of the program?

Answer 3

The problem is indeed in using the factorial function to compute f :

f = factorial(n) / (factorial(n - 2) * 2);

factorial grows very quickly. You implementation exceeds the range of type int for n = 13 . Technically you get undefined behavior, in practice the value computed for f is meaningless, it could even be negative and the division will crash if factorial(n - 2) computes to 0 , which will happen for any value of n larger than 35 .

Here is a much simpler expression which is valid up to n = 46340 :

f = n * (n - 1) / 2;

There are other problems in the code:

• you do not test for scanf_s() failure to read numbers
• you do not test for allocation failure
• using arr[i] = calloc(f, sizeof(char)); would prevent the need for the initialization loops as the indirect 2D matrix would already be initialized to all bits 0.
• num is not modified in the loop while (num <= n) , which makes it an infinite loop, another good explanation for your observations
• k is not used anywhere
• it is unclear what you are trying to achieve. Some comments might help casual readers of your code.