c - 在第二个索引上获取一些垃圾值

Question

我正在尝试使用指针在 C 中计算 HCF。

int-type-Pointer ptr 指向一个整数数组。 我给出的输入是 30,60,18,a。这里的“a”是终止整数列表并中断“while”。

我尝试了 Debug模式，并找到了值:

*ptr = 30
*(ptr+1)= -1163005939  //the garbage that i'm talking of. 
*(ptr+2)= 60
*(ptr+3)= 30

而我应该得到的是 30、60、18。

#include<stdio.h>

void main(){

int* ptr=(int*) malloc( sizeof(int)* 50);
int input=0;
int smallest;

printf ("Enter the numbers (press any alphabet when you're done )\n");

    while (1)
    {   input++;     

        if (input==1 && scanf("%d", ptr))  // the first number is stored in smallest
        {smallest = *ptr; continue;}

        if (!scanf("%d",ptr+input ))   // if the input is a character , scanf says 0, 
        {input--;                      //! makes it 1, and we jump out of  the loop
            break;}                     

        if (smallest > *(ptr+input))  // swapping
        { smallest += *(ptr+input);
            *(ptr+input) = smallest- *(ptr+input);
            smallest= smallest- *(ptr+input);
        }
    }

// code for determining the HCF
char c;

if (smallest <=0)
{
printf("", scanf("%c",&c ), printf("Answer is 0")); // it will print that the answer 
exit(0);                                            //is 0 then waits for you to 
}                                                   //press any key and then it exits

//if smallest greater than 0

int i=2;
int HCF=1;
int j;

for (; i<smallest/2; i++)
    { for (j=0; j<=input;j++)

         // this is where the problem is suspected 
         //as i ve seen in the debug mode 
         //it gives results divides the garbage value to i

       {if (! (*(ptr+j)%i == 0))   // if the number stored in the location is not 
          break;                   //divisible by i, then leave that number i 
        }                          //and check for the next i 

        if (j>input)
        HCF *= i;
    }

    printf( "", scanf("%c", c), printf("The HCF is %d ", HCF)); 
    free(ptr);

}

那么问题是什么？ 而且我不想分配 50 个整数内存。我只想在没有任何分配的情况下疯狂地使用指针。我知道它的不良做法，但我只想应用它。这对其他程序有什么危害吗？怎么办？

Answer 1

它是垃圾，因为您从未向它写入任何内容。看这段代码

while (1)
{   input++;     

    if (input==1 && scanf("%d", ptr))  // the first number is stored in smallest
    {smallest = *ptr; continue;}

    if (!scanf("%d",ptr+input ))   // if the input is a character , scanf says 0, 
    {input--;                      //! makes it 1, and we jump out of  the loop
        break;} 

    //code that doesn't assign values to ptr
}

当您到达 scanf("%d",ptr+input ) 时, input将是 2如果scanf("%d", ptr)返回一个真值。这是因为这个 if 语句:

    if (input==1 && scanf("%d", ptr))  // the first number is stored in smallest
    {smallest = *ptr; continue;}

注意你如何continue这里什么时候input等于1 ？这意味着 while loop 将跳过所有其他内容并从头开始，它要做的第一件事是递增 input。来自 1至 2 .