如何使用php创建一个循环函数？

Question

I'm trying to create what I think are a series of functions that will loop through some code and yield a color. Color result will be base on time range and totals.

Unfortunately, because my skillset in PHP is very low, I have only managed to get to where I'm at by starting off writing out what I wanted, then transition what I wanted into what I think would be the start of the code. This was based on what I understood from the Academy of Code website and a Udemy Course. The end result is for a website. If I could get help on what is below, I'm pretty sure I can take it from there.

If tot_time == 48 mths

If (exp_date >= 0 mths && < 13 mths) && (cred_end == cred_start)
    {
//Make background color red
bkgrd == red;
}

If (exp_date >= 12 mths && < 25 mths) && (cred_end == cred_start)
   {
//Make background color red
bkgrd == red;
}

If (exp_date >= 24 mths && < 37 mths) && (cred_end == cred_start)
   {
//Make background color red
bkgrd == red;
}

If (exp_date >= 36 mths) && (cred_end == cred_start)
   {
//Make background color white
bkgrd == white;
}

If (exp_date >= 0 mths && < 13 mths) && (cred_end == cred_start) / 4
    {
//Make background color red
bkgrd == red;
}

If (exp_date >= 12 mths && < 25 mths) && (cred_end == cred_start) / 4
    {
//Make background color red
bkgrd == red;
}

The expected result is that the date range and completion of the math will yield a color.