add4[x_] := x + 4

Do[a = add4[t];
 If[a == 6 && add4[t + 1] == 7, Break[]], {t, 5}]

a

Clear[add4]
count = 0;

add4[x_] := add4[x] = (count++; x + 4)
Do[a = add4[t];
 If[a <= 6 && add4[t + 1] == 7, Break[]], {t, 5}]

{a, count}