Question: How do i write a "if...then" function in Maple?

Hi all, I'm using text box and push button to create my user interface for my system. I  wish to use a if..then function to check some condition, if the condition is true then do statement and print out in the text box. When is key coding in the push button and click the push button, then if ...then function not working and the result that not suitable for the condition also have been printed out in text box.So,can someone help my to solve the problem?

Here in the coding i did

use DocumentTools in 

Do (C = %txtC);
Do (p = %txtpk1);
Do (q = %txtpk2);
Do (d = %txtpk3);
Do (A1 = %txtA1);
Do (A2 = %txtA2);
Do (w = `mod`((C*d), A2));
Do (mp = `mod`(w^((p+1)*(1/4)), p));
Do (mq = `mod`(w^((q+1)*(1/4)), q));
Do (hl = `mod`((mp-mq)/p, q));
Do (h2 = `mod`((-mp-mq)/p, q));
Do (m1 = mp+(hl*p));
Do (m2 = mp+(h2*p));
Do (m3 = (p*q)-m1);
Do (m4 = (p*q)-m2);
if m1 <= 2^(2*k-1) then t1 := (C+(-A1*(m1^2)))/A2 end if;
Do (t1);
if m2 <= 2^(2*k-1) then t2 := (C+(-A1*(m2^2)))/A2 end if;
Do (t2);
if m3 <= 2^(2*k-1) then t3 := (C+(-A1*(m3^2)))/A2 end if;
Do (t3);
if m4 <= 2^(2*k-1) then t4 := (C+(-A1*(m4^2)))/A2 end if;
Do (t4);

Do (%txtw = w);
Do (%txtm1 = m1);
Do (%txtm2 = m2);
Do (%txtm3 = m3);
Do (%txtm4 = m4);
Do (%txtt1 = t1);
Do (%txtt2 = t2);
Do (%txtt3 = t3);
Do (%txtt4 = t4);
end use; 
 

Thabk you.