How to fix compiler error: CS0841 - Cannot use local variable before it is declared, when variable has already been declared outside the loop

I get a CS0841 compiler error for 3 different variables that are already initialized outside their respective conditional statements. At first I thought it was a simple issue of having my brackets in the wrong place but after double checking my code, it looks like the code within the loop just doesn't recognize the initialization of the variable outside the loop or if statement. Why do I get this issue?

//Simplified version of the code. It doesn't make as much sense simplified but this highlights my //issues more clearly. 

if(R > 10) { 
int [,] MRold = new int[R, 14]; // MRold is declared here. 
//rest of if statement.....
}
else{
//the else condition......
}

int k = 1; //k is declared.

for(int i = 0; i < MRarray.GetUpperBound(0); i++) {
    if(R > 10) {
        for(int j = 0; j < MRold.GetUpperBound(0); j++) { //MRold here throws the 0841 error
            int oo; //oo declared
            for(int CC = 8; CC <= Rows; CC++) {
                oo = CC;
                break;
            }
            // A couple other conditional statements/loops here, and nested within them is this:
                for(int jj = 2; jj <= 14; jj++) { 
                    OutArray[k, jj] = OutArray[k, jj] + Increment; // k throws the error
                    OutArray2[oo, jj] = OutputArray2[oo, jj] + Increment; // oo throws error.
                    break;
                }
            // I close the aforementioned other loops/statements here.
        }
    }
}
//Basically my issue is the innermost loops can't access the declared variables within outer 
//loops or loops/conditions that came before the one they are nested in.
//Also want to note that instances of MRold/oo/k that occur after the very first one that throws the //error don't throw an error. Only the first instance of the declared variable throws an error //within the loop/conditional statement. The rest of the instances do not throw the same error. 
//They compile fine.

The quick amendment is to initialize oo, e.g.

// Rain or shine, oo is assigned 
int oo = 0;

for (int CC = 8; CC <= Rows; CC++) {
  // oo can be change under some conditions
  oo = CC;

  break;
}

...

// oo is guaranteed to have a value assigned
OutArray2[oo, jj] = OutputArray2[oo, jj] + Increment;

since compiler doesn't understand that since for loop will be run at least once, oo will be assigned before its first usage. The next stage is to think on do you want the for loop at all? You break just after the entry: int CC = 8; ... oo = CC; break;, why don't you put it as

int oo = 8;

Check if Increment is assigned as well (I can't see Increment declaration in your code)