This program illustrates the use of the STL swap() algorithm to swap
integer values, double values, and string values in simple variables.
It also illustrates the swapping of integer values in a vector, using
three different ways to access the values.
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Swapping integer values in simple variables:
Before swap(i1, i2) i1 = 12     i2 = -3
After  swap(i1, i2) i1 = -3     i2 = 12
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Swapping double values in simple variables:
Before swap(x1, x2) x1 = 4.3    x2 = 17.5
After  swap(x1, x2) x1 = 17.5   x2 = 4.3
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Swapping string values in simple variables:
Before swap(s1, s2) s1 = Hello  s2 = Good-bye
After  swap(s1, s2) s1 = Good-bye  s2 = Hello
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Now we display the values from a vector of integers. Then we swap the first
and last values, the second and second last values, and the third and third
last values. Each time we do a swap, we use a different way of accessing the
values being swapped.
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Here are the integer values from the vector:
1 2 3 4 5 6 7 8
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First we make the call swap(v.at(0), v.at(v.size()-1).
Here are the vector values with the first and last ones swapped:
8 2 3 4 5 6 7 1
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Next we make the call swap(v[1], v[v.size()-2]).
Here are the vector values with the 2nd and 2nd-last ones swapped:
8 7 3 4 5 6 2 1
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Finally we make the call swap(*(v.begin()+2), *(v.end()-3)).
Here are the vector values with the 3rd and 3rd-last ones swapped:
8 7 6 4 5 3 2 1
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