我的方法似乎总是返回FALSE

This method:

这个方法:

- (BOOL)checkForDigits {
    NSString *editableExpression = self.expression.text;
    for (int i = 0; i < editableExpression.length; i++){
        char charAtPosition = [editableExpression characterAtIndex:i];
        for (int c = 0; c < 10; c++ ){
            char digitAtPosition = digits[c];
            if (charAtPosition == digitAtPosition){
                return TRUE;

            }
            else {
                return FALSE;
            }
        }
    }
}
- (BOOL)checkForDigits {