1-2 NL. Player A bets $50. Player B goes all in for $76. Player C doesn't announce raise and bets $100. Is player C's bet just a call or a raise? If a raise, what is his min raise amount and why?
It really depends on the card room and the rules they play, there is no definitive "Everyone must play like this" rule. You can find some "official" rules out there but these are generally rules enforced by different poker institutions and are not universal.
Some rooms enforce that you must declare your intent before throwing chips into the pot with penalties. Such penalties may be turning the chips to dead money and folding your hand or forcing you to call in this situation. Here in general Player C would have been forced to call and received change out of the pot from the dealer.
Other rooms will force player C to raise here even if he was just going to call because he has put more in the pot than the previous bet or raise.
In general the most common rule is that you must declare your intent. Here is an example of the TDA rule set for calling:
Now again depending on the card room your playing at some force your raise to be double the last raise, so in this case Player C would have to raise a minimum of $152. Others do not and as long as your raise exceeds the previous bet by at least 1 blind the bet is valid. Others rooms will force Player C to exceed the current pot size or at least a percentage of the current pot. So in this case he would have to raise $126 or more.
If you are ever in doubt, always speak to the dealer or the floor-man about the house rules before taking an action your unsure of.
I assume your example is a live Game. In that case, where I come from, player C merely calls when he silently tosses in any amount in a single motion/single bet without specifically voicing his it intention to raise.
I know that depending on your locale, the ruling may be vastly different, however next you find yourself in CT, keep tbe above in mind.