How do I resize and populate an array using price values?

Question

I’m looking for some help in methods to vary the size of an array which is automatically filled with data.

For example, I would like to plot a chart of EMA values with a user input to choose how many x-values are displayed.

I can do this manually, say by deciding to plot 5 values:

double x_axis[] = {1,2,3,4,5};
double y_axis[] = {ema[5],ema[4], ema[3], ema[2], ema[1]};

But say for example I wanted 100 values on the x-axis, how could I automate this?

Would I use a for loop using the input value?

Please help!