[C ++ header files commonly used functions] <algorithm> in the usual function (absolute value, exchange, comparison)

swap(a,b)

　　For exchanging a, b and two variables;

max(a,b)

　　Returns a, b is the maximum;

min (a, b)

　　Returns a, and b is the minimum value;

abs(x)

　　Returns the absolute value of x, x must be an integer;