Scanf doesn't work well with while loop

Question

So I have the following code:

void main(int argc, char **argv)
{
    int loggedIn=0;
    char *currentCommand;

    while (!loggedIn)
    {
    printf("Enter your command:");
    scanf("%s",currentCommand);
    printf("\n%s\n",currentCommand);
    }
}

The problem is scanf() works well the first time, then is starts reading (null) and the output would be Enter your command: (null) in an infinite loop.

I want to input more commands and stop when I change the value of loggedIn, but once I input one command, it starts printing Enter your command: (null) endlesly.

Answer 1

您需要使用malloc将内存分配给currentCommand指针（并在末尾释放它）或在开始时为其分配大小，例如

char currentCommand[256];

Answer 2

currentCommand is pointer variable who will save address(which is integer) of char type variable and have a size of 4 bytes (32 bit machine).

Now when you write ℅s in scanf you are supposed to pass address of char array.(which you haven't declared), so scanf will take the address (value saved in currentCommand which is garbage).

Answer 3

The most important thing while using character pointers is you can create a character array at the time of declaration ie,

char *p="Hello World";

This creates memory in data/code section which is read only section.

And you cannot create a character array with scanf() function. Should have to use dynamic memory allocation or initialize as above