Write at least $3$ different C$++$ statements that each add $1$ to integer variable x$.$

c$)$ Repeating a set of instructions a specific number of times is called $\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$ repetition.

d$)$ When it is not known in advance how many times a set of statements will be repeated, a$($n$)\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$ value can be used to terminate the repetition.