运行下面代码会出现如下警告：choosing\choosing\5.8.c(26): warning C4244: “=”: 从“double”转换到“float”，可能丢失数据
求大神解释一下是什么原因，我并没有定义double型变量啊



#include <stdio.h>
void main()
{
    float b1, b2, b4, b6, b10,d;
    long int i;
    int c;
    b1 = 100000 * 0.1;
    b2 = b1 + 100000*0.075;
    b4 = b2 + 200000*0.05;
    b6 = b4 + 200000*0.03;
    b10 = b6 + 400000*0.015;
    scanf_s("%ld", &i);
    if (i >1000000)c = 10;
     else c = i / 100000;
    switch(c)
    {
        case 0:d = i*0.1; break;
        case 1:d = b1 + (i - 100000)*0.075; break;
        case 2:
        case 3:d = b2 + (i - 200000)*0.05; break;
        case 4:
        case 5:d = b4 + (i - 400000)*0.03; break;
        case 6:
        case 7:
        case 8:
        case 9:d = b6 + (i - 600000)*0.015; break;
        case 10:d = b10 + (i - 1000000)*0.01; break;
    }
    printf("%5.2f", d);
}

thank you