If statement not being entered

So I'm going to post a big section of code just so you can see what I'm working with.

char isbnHold[13]; /* holds isbn to do calculations */
strncpy(isbnHold,structBuffer.isbn,13); /* copies isbn into hold */

    if((checkISBN(isbnHold))==0){
    printf("made it in");
    int k;
    int checkInt;
    for(k=0;k<4;k++){
        if(strcmp(structBuffer.isbn,structArray[k].isbn)!=0){
            checkInt=1;
            printf("Or did something go wrong here?");
        }
        else if(strcmp(structBuffer.isbn,structArray[k].isbn)==0){
            checkInt=0;
            printf("Did we get to here?");
            k=5;
        }
    }
    if(checkInt==0){
        if(structBuffer.requestType == Query){
            printf("is it getting here?\n");
            int i;
            for(i=0;i<4;i++){
                if(strcmp(structBuffer.isbn,structArray[i].isbn)==0){
                    returnStruct.respType = Okay;
                    returnStruct.requestID = structBuffer.requestID;
                    strncpy(returnStruct.isbn,structArray[i].isbn,13);
                    strncpy(returnStruct.authors,structArray[i].authors,100);
                    strncpy(returnStruct.title,structArray[i].title,100);
                    returnStruct.edition = structArray[i].edition;
                    returnStruct.year = structArray[i].year;
                    strncpy(returnStruct.publisher,structArray[i].publisher,100);
                    returnStruct.inventory = structArray[i].inventory;
                    returnStruct.available = structArray[i].available;
                }
            }
        }
        else if(structBuffer.requestType == Borrow){
            int j;
            for(j=0;j<4;j++){
                if(strcmp(structBuffer.isbn,structArray[j].isbn)==0){
                    if(structArray[j].available > 0){
                    returnStruct.respType = Okay;
                    returnStruct.requestID = structBuffer.requestID;
                    strncpy(returnStruct.isbn,structArray[j].isbn,13);
                    strncpy(returnStruct.authors,structArray[j].authors,100);
                    strncpy(returnStruct.title,structArray[j].title,100);
                    returnStruct.edition = structArray[j].edition;
                    returnStruct.year = structArray[j].year;
                    strncpy(returnStruct.publisher,structArray[j].publisher,100);
                    returnStruct.inventory = structArray[j].inventory;
                    returnStruct.available = structArray[j].available;
                    structArray[j].available = (structArray[j].available-1);
                    }
                }
                else{
                    returnStruct.respType = AllGone;
                }
            }
        }
        else if(structBuffer.requestType == Return){
            int x;
            for(x=0;x<4;x++){
                if(strcmp(structBuffer.isbn,structArray[x].isbn)==0){
                    returnStruct.respType = Okay;
                    returnStruct.requestID = structBuffer.requestID;
                    strncpy(returnStruct.isbn,structArray[x].isbn,13);
                    strncpy(returnStruct.authors,structArray[x].authors,100);
                    strncpy(returnStruct.title,structArray[x].title,100);
                    returnStruct.edition = structArray[x].edition;
                    returnStruct.year = structArray[x].year;
                    strncpy(returnStruct.publisher,structArray[x].publisher,100);
                    returnStruct.inventory = structArray[x].inventory;
                    returnStruct.available = structArray[x].available;
                    structArray[x].available = (structArray[x].available+1);
                }
            }
        }
    }
    else if(checkInt==1){
        returnStruct.respType = NoInventory;
    }
}

I realize this is a lot to look at but if it is a syntax error I it is probably necessary to have it all. As you can see I'm checking the value of a function. I know that this value is 0 because at one point I had a printf statment to tell me what the value of it was. However you can see the other printf statements I am using to debug and none of those are being printed. I don't know why it is skipping this block but any help would be appreciated. It enters the else if block of the return value being 1 if an invalid ISBN entered.