Variable inside if statement in javaScript

I wonder why my first code doesn't work and the second does. I thought they're basically the same.... Looks like var inside if statement doesn't seem to be processed as expected. Could anyone please clarify why it doesn't work?

var myFarm = ["chickens", "pigs", "cows", "horses", "ostriches"];
var letterCheck = myFarm[i].charAt(0);

for (var i = 0; i < myFarm.length; i++) {
    console.log(i);
}

if (letterCheck === "c" || letterCheck === "o") {
    alert("Starts with 'c' or 'o'!");
}

---

var myFarm = ["chickens", "pigs", "cows", "horses", "ostriches"];
var arrayLength = myFarm.length;


for (var j = 0; j < arrayLength; j++) {

    console.log(myFarm[j]);


    if (myFarm[j].charAt(0) === "c" || myFarm[j].charAt(0) === "o") {

        alert("Starts with a c or an o!");
    }

}