小编Dr *_*pec的帖子

为什么在scanf()程序中的格式说明符之前使用空格时工作正常呢？代码如下:

printf("What's your username: ");
scanf(" %s", username);

printf("Do you want to make a deposit or a withdrawal? [d/w]\n");
scanf(" %c", &choice);

当我没有像下面这个代码的空格时,它会退出:

printf("What's your username: ");
scanf("%s", username);

printf("Do you want to make a deposit or a withdrawal? [d/w]\n");
scanf("%c", &choice);

对此有一个很好的解释吗？