This program illustrates a vector of vectors.
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We create, populate, and then display, a vector (of size 3) of integer vectors.
Each "row" of the "vector of vectors" has a different length, so the overall
effect is to have a two-dimensional "jagged array" of integers.
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The first row has 4 components, the second has 10, and the third has 6:
7 7 7 7
3 3 3 3 3 3 3 3 3 3
5 5 5 5 5 5
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