how to use "gonna" & "gotta"

1. be gonna = be going to，口语常见用法，注意前面要有be，后面跟动词原形。
    Are you gonna be there if I was down? 我失意的时候你会在吗？('N Sync: Are You Gonna Be There)
    I'm gonna run away and never say goodbye. 我要逃掉，不辞而别。(Linkin Park: Runaway)
    I am gonna be there at 3:00. 我三点时会到那.
    (这句话也可以说成, "I am going to be there at 3:00." 或是 "I will be there at 3:00." 也是蛮常用的. 此外, 老美也喜欢说, "I will catch you there." 例如二个人约好要在体育馆见面, 你就可以说, "I'll catch you in the gym.")

2.gotta=got to (相当于have to 不得不，必须)
    There's something I gotta tell ya我有点事要和你说.
    I've gotta get outta here.我得离开这儿了。
    I've gotta catch the bus. 我要去赶公共汽车了。