C 学生作业， ‘%f’ 需要类型为 ‘float ’ 的参数，但参数 2 的类型为 ‘double ’

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我正在做作业，我收到了这个警告:

C4_4_44.c:173:2: warning: format ‘%f’ expects argument of type ‘float *’, 
but argument 2 has type ‘double *’ [-Wformat]

变量在 main 中声明为:

double carpetCost;

我将函数调用为:

getData(&length, &width, &discount, &carpetCost);

函数如下:

void getData(int *length, int *width, int *discount, double *carpetCost)

{

    // get length and width of room, discount % and carpetCost as input

    printf("Length of room (feet)? ");

    scanf("%d", length);

    printf("Width of room (feet)? ");

    scanf("%d", width);

    printf("Customer discount (percent)? ");

    scanf("%d", discount);

    printf("Cost per square foot (xxx.xx)? ");

    scanf("%f", carpetCost);

    return;

} // end getData

这让我抓狂，因为书上说你不要在