Before we can talk about Repentance for sin we must determine what sin is.

According to Merriam Webster:

SIN, in the form of a noun

The voluntary departure of a moral agent from a known rule of rectitude or duty, prescribed by God;
any voluntary transgression of the divine law, or violation of a divine command; a wicked act;
 iniquity. Sin is either a positive act in which a known divine law is violated, or it is 
the voluntary neglect to obey a positive divine command, or a rule of duty clearly implied 
in such command. Sin comprehends not action only, but neglect of known duty, all evil thoughts
purposes, words and desires, whatever is contrary to God's commands or law. 1st John 3. 
Mattthew 15. James 4. Sinner neither enjoy the pleasures of nor the peace of piety. Among divines, 
sin is original or actual. Actual sin, above defined, is the act of a moral agent in violating 
a known rule of duty. Original sin, as generally understood, is native depravity of heart to
 the divine will, that corruption of nature of deterioration of the moral character of man, 
which is supposed to be the effect of Adam's apostasy; and which manifests itself in moral agents
by positive act of disobedience to the divine will, or by the voluntary neglect to comply with 
the express commands of God, which require that we should love God with all the heart and soul
and strength and mind, and our neighbor as ourselves. This native depravity or alienation of affections
 from God and his law, is supposed to be what the apostle calls the carnal mind or mindedness, 
which is enmity against God, and is therefore denominated sin or sinfulness.

SIN, When used in the form of a verb.

1. To depart voluntarily from the path of duty prescribed by God man; to violate the divine law in
any particular, by actual transgression or by the neglect or non-observance of its injunctions; to 
violate any known rule of duty. 

2. To offend against right, against men or society; to trespass. 

In your question your use of the word indicates that you are using the verb form. In its verb form there are two types of sin intentional and unintentional.

Intentional sin is what Adam committed because he knew that he was disobeying God and did it anyway. Eve on the other hand was beguiled by the Serpent, and sinned out of her deception.

In your question you are asking about intentional sin, because you state that it is an act with the expectation that if you repent it will be forgiven.

As to whether or not that sin will be forgiven if you repent the answer is yes, but you must first understand what repentance is; Repentance is much more than saying you are sorry.

According to Merriam Webster

REPENT'ANCE, n.

1. Sorrow for any thing done or said; the pain or grief which a person experiences in consequence
of the injury or   inconvenience produced by his own conduct.

2. In theology, the pain, regret or affliction which a person feels on account of his past conduct,
because it exposes him to punishment. This sorrow proceeding merely from the fear of punishment,
is called legal repentance, as being excited by the terrors of legal penalties, and it
may exist without an amendment of life.

3. Real penitence; sorrow or deep contrition for sin, as an offense and dishonor to God, 
a violation of his holy law, and the basest ingratitude towards a Being of infinite benevolence.  

This is called evangelical repentance, and is accompanied and followed by amendment of life.

Repentance is a change of mind, or a conversion from sin to God.

Matthew 4:17 KJV From that time Jesus began to preach, and to say, Repent: for the kingdom of heaven is at hand.

The word in the original Greek was:

μετανοέω metanoeo (met-an-o-eh'-o) v. to think differently or afterwards, 
i.e. reconsider (morally, feel compunction)

So the actual word used by Jesus means Afterward, and actually has to do with real sorrow at offending God (or to feel righteous regret) Just feeling guilty for what you have done is not true Repentance. True repentance has to do with feeling guilty at disobeying God's commands.

To feel guilty for wrong doing and getting caught is not the same as feeling guilty just because you committed the act, even though no one else ever knows that you did.

consider this from Paul to the Corinthians:

2nd Corinthians 7:8 through 11 KJV

For though I made you sorry with a letter, I do not repent, though I did repent: for I perceive that the same epistle hath made you sorry, though it were but for a season. Now I rejoice, not that ye were made sorry, but that ye sorrowed to repentance: for ye were made sorry after a godly manner, that ye might receive damage by us in nothing. For godly sorrow worketh repentance to salvation not to be repented of: but the sorrow of the world worketh death. For behold this selfsame thing, that ye sorrowed after a godly sort, what carefulness it wrought in you, yea, what clearing of yourselves, yea, what indignation, yea, what fear, yea, what vehement desire, yea, what zeal, yea, what revenge! In all things ye have approved yourselves to be clear in this matter.

Repentance is the relinquishment of any practice, from conviction that it has offended God.

True repentance then is to quit doing wrong strictly because it offends God and not for your sake.

So will you sin again the answer is yes you will, but once you receive Salvation; your sins should only be unintentional sin. Therefore the answer to you question has to be if you premeditate and decide to sin you must not only repent, but repent for the right reason, or as most Christians put it you must truly repent.

Another important aspect of turning-away-from-sin is the source of strength to accomplish this.

As long as we think that we ourselves (our intelligence, our will, our bible knowledge) are the source of strength, we will never be truly freed from sin.

Remember, sin is not only doing something, but also thinking, formulating, and attitude -- which are the sins that we do in our minds (read the list in Galatians 5:19-21, how many of those acts of sin are in our minds).

For instance, it is far easier to decide not to hit another person again compared to deciding not to envy again. Hitting another person is a physical act, envy is in our minds and hearts, but when we harbor envy, not only we sin in our mind, but left unchecked, the sin will grow and manifest itself in physical acts like verbal abuse, which in the end is just as damaging or even more so compared to physically hitting someone.

Therefore, the sins that we commit in our minds and hearts are far more insidious. And we are powerless to stop them on our own strength, only God can guard us when we are in fellowship with Him. This is why the concept of being in fellowship with God (defined well by @mojo's answer) is so important for us Christians.