How To Think Like a Computer Scientist C++ Edition The Pretext Interactive Version

It is often useful to take the data from the previous tables and store them for later access, rather than just print them. What we need is a way to store 10 integers. We could create 10 integer variables with names like howManyOnes, howManyTwos, etc. But that would require a lot of typing, and it would be a real pain later if we decided to change the range of values.

A better solution is to use a vector with size 10. That way we can create all ten storage locations at once and we can access them using indices, rather than ten different names. Here’s how:

int numValues = 100000;
int upperBound = 10;
vector<int> vector = randomVector(numValues, upperBound);
vector<int> histogram(upperBound);

for (int i = 0; i < upperBound; i++) {
  int count = howMany(vector, i);
  histogram[i] = count;
}

I called the vector histogram because that’s a statistical term for a vector of numbers that counts the number of appearances of a range of values.

The tricky thing here is that I am using the loop variable in two different ways. First, it is an argument to howMany, specifying which value I am interested in. Second, it is an index into the histogram, specifying which location I should store the result in.