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There are more than twenty mathematical functions declared in <math.h>; here are some of the more frequently used. Each takes one or two double arguments and returns a double.
sin(x)  sine of x, x in radians
cos(x)  cosine of x, x in radians
atan2(y,x) arctangent of y/x, in radians
exp(x)  exponential function ex
log(x)  natural (base e) logarithm of x (x>0)
log10(x)  common (base 10) logarithm of x (x>0)
pow(x,y)  xy
sqrt(x)  square root of x (x>0)
fabs(x)  absolute value of x

The function rand() computes a sequence of pseudo-random integers in the range zero to RAND_MAX, which is defined in <stdlib.h>. One way to produce random floating-point numbers greater than or equal to zero but less than one is (more…)

The UNIX operating system provides its services through a set of system calls, which are in effect functions within the operating system that may be called by user programs. (more…)

In the UNIX operating system, all input and output is done by reading or writing files, because all peripheral devices, even keyboard and screen, are files in the file system. This means that a single homogeneous interface handles all communication between a program and peripheral devices. (more…)