The specific ideas are as follows:

Multiply this number by 100 to make the third place after the decimal point the first place;

The rounding of C language is a community decimal, not a rounding. At this time, adding 0.5 to the number can achieve the rounding effect without calling any rounding function.

The implementation code and comments are as follows:

Invalid? Master ()

{

Double? num = 3. 14 159； ? //Here we use the value distance of pi.

num=？ (int)(num * 100+0.5)； ? //Multiply by 100+0.5 and round it off.

printf("%.3lf "，num)； ? //output results

}