Simple c
Today is the second day, and I have finished reading Chapter 3.
Given the length of the three sides of the triangle, find the area of the triangle. 
Here, we can write the program very simply based on the simple triangle mathematical calculation formula, but the difference from the previous one is that there is a math.h and %lf new things, which will be written in the following blog.
Now let’s add what functions are included in the math.h file:
- int abs (int x): find the absolute value of the integer x
- double fabs (double x): find the absolute value of x
- double cos (double x): find the value of cos (x)
- double exp (double x): find the value of x in e
- double floor (double x): find the largest integer not greater than x
- double log（double x）：求ln（x）
- double log10（double x）
- double pow (double x, double y): Calculate the value of x times y
- double sqrt (double x): calculate the root number