scanf[^\n] in a loop , not stop to wait for user input except for 1st time

See more:

C

I need to use scanf("%[^'\n']" to input a sentence. And the input is in a loop, I have other code block to process it.

If I just use scanf(%s) other than ^\n,each time loop the console will stop to wait user input, that's correct routine I need.

However, if I use scanf(%[^\n] or %[^'\n'], only the 1st time the console wait for user input, then it will continue display printf("Input:") continuously without stop to wait the new input.

I tried assign array to null, free array space, flush stream, not helpful.

Simple sample code and sample incorrect output:

#include <stdio.h>

void userInput(){

  char* in;
  in=malloc(sizeof(char)*20);
  printf("Input: ");
  scanf("%[^'\n']",in);
  fflush(stdin);
  free(in);
}

void main(void) {

  for(;;)
    userInput();
}</stdio.h>

Sample Malfunction output:

Input:I enter something
Input: Input: Input:........Input