[SOLVED] How to check if a String contains a specific number

[odometer]

@LuXian

So I found a simple "oled calendar" code on github and I want to add a simple square to highlight the current date of the month but I don't know how to do it. I was thinking of maybe testing the Strings "week1", "week2", etc... if it contains the current date then it will supposedly output a true or false then from there plot it with x,y coordinate system. So my question is how to check or test if a String contains a specific number?

This is an excellent example of an XY problem. (What is an XY problem? See: https://xyproblem.info/ )

You don't need to test any strings. You just need to know where in the grid a specific date will be located.
To begin, suppose that today is the 1st day of the month. Then today's date will, naturally, appear in the row for week1, in the position (0 to 6) given by startDay.
OK, so we've just solved our problem for the 1st day of the month. What if it is the 2nd day of the month? We just start with startDay, and move forward 1 position. If this moves us off the end of the row, then we have to start again at the beginning of the next row.
For the 3rd day of the month, we have to move forward one more position, so we will be 2 positions past startDay. And so forth, for the remaining days of the month. In general, on day N, we will be N-1 positions past 'startDay'. In code, that would look something like this:

int rowNumber = 1; // rows are numbered 1 to 5
int colNumber = startDay; // columns are numbered 0 to 6
colNumber += (now.day() - 1); // advance the column by the appropriate number of days
while (colNumber > 6) { // check if we are past the end of the row
  colNumber -= 7; // move backwards 7 columns
  rowNumber++; // advance to the next row
}
if (rowNumber > 5) {
  rowNumber = 1;
}