What do you not understand or find in the manual?
You have two strings as you said, string1 in your code with a given value and one for the inkey:

STRING* string1 = "1234";
STRING* string2 = "#4"; // String for the inkey
...

after the inkey you can compare this two strings:

if(str_cmp(string1,string2))
{
... // this code runs if string1 = string2
}