Part of this assignment includes printing out on the display the current equation that is present to be solved, for that I use the following methods:
+ (NSString *)descriptionOfTopOfStack:(NSMutableArray *)stack {
NSMutableString *programFragment = [NSMutableString stringWithString:#""];
id topOfStack = [stack lastObject];
if (topOfStack) [stack removeLastObject];
if ([topOfStack isKindOfClass:[NSNumber class]]) {
[programFragment appendFormat:#"%g", [topOfStack doubleValue]];
} else if ([topOfStack isKindOfClass:[NSString class]]) {
NSString *operation = topOfStack;
if ([self isDoubleOperandOperation:operation]) {
[programFragment appendFormat:#"(%# %# %#)", [self descriptionOfTopOfStack:stack], operation, [self descriptionOfTopOfStack:stack]];
} else if ([self isSingleOperandOperation:operation]) {
[programFragment appendFormat:#"%#( %# )", operation, [self descriptionOfTopOfStack:stack]];
} else if ([ self isNoOperandOperation:operation]) {
[programFragment appendFormat:#"%#", operation];
} else if ([self isVariable:operation]) {
[programFragment appendFormat:#"%#", operation];
}
}
return programFragment;
}
+ (NSString *)descriptionOfProgram:(id)program {
NSMutableArray *stack;
if ([program isKindOfClass:[NSArray class]]) {
stack = [program mutableCopy];
}
return [self descriptionOfTopOfStack:stack];
}
My program computes the results and everything just fine, the only problem is that when I enter a variable, digit or single operand operation the display only shows said last entry, because it doesn't continue to iterate over the rest of the values present in the array, because no other recursive calls are made, any idea how I can make the program execute throughout the entire stack and not have it break the output?
I am not quite sure what you mean. The recursion should stop at a variable, digit or single operand operation. Although for a sin(operand) operation it should continue with the operand.
Did you take into account that your stack might be not completely defined?
Say you enter: 3 Enter 5 + 6 Enter 7 * 9 sqrt
this should translate to: 3+5, 6, sqrt(7*9)
So you have three elements still on your stack, but your approach stopped at sqrt(7*9).
You need to add a check at the to see if there is anything left on the stack, and continue if necessary (and add the comma's).
OK, another hint then (to be added at the end):
if ([stack count]) { // did I finish the entire stack?
[programFragment appendFormat:#"%#, %#", [self describeStack:stack], programFragment];
}
Interestingly you have used a NSMutableString, I did it with a NSString and used the class method stringWithFormat. So each time my result is a new string. I do not know if either approach is better.
aleene already answered, but just to clarify. I added the [stack count] check in the method that calls the recursive function.
+ (NSString *)descriptionOfProgram:(id)program {
NSMutableArray *stack;
NSString *strDesc = #"";
if ([program isKindOfClass:[NSArray class]]) {
// Make a consumable, mutable copy:
stack = [program mutableCopy];
}
while (stack.count) {
strDesc = [strDesc stringByAppendingString:[self descriptionOfTopOfStack:stack]];
if (stack.count) {
// More statements still on stack. We will loop again, but first, append comma separator:
strDesc = [strDesc stringByAppendingString:#", "];
}
}
return strDesc;
}
Related
When parsing API responses, sometimes I can not rely on strings being embedded in quotation marks. ID's are a good example of this, where some API's will send the numerical ID as a string while some will send it as a number.
What is a good practice when parsing such a value? If I simply parse it to an NSString like so:
NSString *myID = (NSString *)message["myID"];
I can end up with an NSString object that somehow contains (long)123.
And using stringValue would cause issues when the value is actually already sent as a string (since NSString does not have a stringValue function).
A way that works, but is somewhat ugly, is this:
id myID = (NSString *)message["myID"];
if ([myID respondsToSelector:#selector(stringValue)])
{
myID = [myID stringValue];
}
You could do something like:
id myID = message["myID"];
if ([myID isKindOfClass:[NSString class]]) { ... }
else { ... }
As long as this logic is encapsulated inside data parser and is opaque for your api users (i.e. they will always get a string) any approach is fine, e.g.:
- (NSString*)parseID:(NSDictionary*)message {
id rawID = message["myID"];
if ([rawID isKindOfClass:[NSString class]]){
return rawID;
} else if ([rawID isKindOfClass:[NSNumber class]]) {
return [(NSNumber*)rawID stringValue];
} else {
// We might still want to handle this case.
NSAssert(false, #"Unexpected id type");
return nil;
}
}
Alternative is to define stringValue in extension, so any possible objet will respond to selector:
#implementation NSString(JSONStringParsing)
- (NSString *)stringValue {
return [self copy];
}
#end
Why not just use description?
NSArray *objects = #[
#NSIntegerMin,
#NSIntegerMax,
#"123456789"
];
for (id object in objects) {
NSString *stringObject = [object description];
NSLog(#"%# -> %# | %#", [object className], [stringObject className], stringObject);
}
I'm checking is first letter of string is 0, if it is remove it and call again method to check is there is still 0. I've debugged this and it seems like when it accomplish number without 0, it goes backwards. Code:
-(NSString *)deleteZerosOnFirst:(NSString *)card
{
NSString *firstLetter = [card substringToIndex:1];
if ([firstLetter isEqualToString:#"0"]) {
card = [card substringFromIndex:1];
[self deleteZerosOnFirst:card];
NSLog(#"CARD: %#", card);
return card;
}
else {
NSLog(#"CARD: %#", card);
return card;
}
}
The main problem is that you're not using the result of the recursion. The line of code where you call yourself should say this:
card = [self deleteZerosOnFirst:card];
Also, you're calling deleteZerosOnFirst before you do the NSLog. Reverse the order of these two lines. That will at least give you your debug output in the right sequence.
Here's your recursive call:
[self deleteZerosOnFirst:card];
That doesn't modify the string that card references. It creates and returns a new string. You're ignoring the returned string. You want this:
card = [self deleteZerosOnFirst:card];
But this is really a lot simpler:
#implementation NSString (withoutLeadingZeroes)
- (NSString *)withoutLeadingZeroes {
NSString *s = self;
while ([s hasPrefix:#"0"]) {
s = [s substringFromIndex:1];
}
return s;
}
#end
Any one please help me to understand the String comparison technique in Objective-C
NSString *strNew1 = #"AA";
NSString *strNew2 = #"AA";
So to compare both the strings we could use,
Method 1. if (strNew1 == strNew2) {
NSLog(#"Equal");
}
or
Method 2: if ([strNew1 isEqualToString:strNew2]) {
NSLog(#"Equal");
}
In this condition both of them are success. But am aware that method 1 will get failed at certain other condition. And also I have tried the below conditions(All are success).
NSString *strNew = #"AA";
NSString *strNew1 = #"AA";
NSString *strNew11 = [[NSString alloc] initWithString:strNew1];
NSString *strNew3 = strNew;
NSArray *arr = #[#"AA"];
NSString *strNew4 = [arr objectAtIndex:0];
NSString *strNew5 = [arr objectAtIndex:0];
_test = strNew5;
_test1 = #"AA";
if ([strNew isEqualToString:strNew1]) {
NSLog(#"Equal");
}
if (strNew == strNew3) {
NSLog(#"Equal1");
}
if (strNew == [arr objectAtIndex:0]){
NSLog(#"Equal2");
}
if (strNew == strNew4){
NSLog(#"Equal3");
}
if (strNew5 == strNew4){
NSLog(#"Equal4");
}
if (strNew4 == [arr objectAtIndex:0]){
NSLog(#"Equal5");
}
if (strNew11 == [arr objectAtIndex:0]){
NSLog(#"Equal11");
}
if (self.test == strNew4){
NSLog(#"Equal3");
}
if (self.test == self.test1){
NSLog(#"Equal3");
}
TEST *test = [TEST new]; // Tried with a class with NSString property with value "AA" . (test.strTest value is #"AA")
if (strNew == test.strTest) {
NSLog(#"Equal"); //success
}
I knew most of them are redundant. Am not able to understand the basics behind this. Please anyone give clear explanation on the concept behind this. Thanks.
In the cases you defined the strings created are internally treated as string literals. The runtime will not allocate different memory space to such strings.
Essentially all the strings that contain the same string literal ("AA" in your case) will point to the same memory location. This is done as a part of memory optimization by Apple.
When you change the value of any string (say to "AB") a new address will be allocated to that NSString object and then == will fail.
You need to use below instance method of NSString class.
- (BOOL)isEqualToString:(NSString *)aString;
So, In your case simply follow below:
if ([strNew isEqualToString strNew4]){
NSLog(#"Equal3");
}
By doing (strNew == strNew4),
You are only comparing the addresses of the objects.
The first way compares pointers, while the second way compares objects.
That is, the first way compares if the pointers have the same value. In this case it is likely that they don't, in the second case the objects will be compared. Since they are initialized the same way they could be equal. (Note, it appears that with the UIButton's implementation of isEqual: the result is always false.)
In most cases using == is not what you want. However, what is appropriate depends on your objective.
if (strNew1 == strNew2) //This compared your pointers
{
}
and
if ([strNew1 isEqualToString:strNew2]) //Compares NSString object
{
}
Remember that isEqualToString: comes with a WARNING
[string1 isEqualToString: string2]
will effectively return false is both strings are nil.
I am trying to get the last NSString from a NSMutableArray, and delete it if it's empty.
Here is the code I am using:
- (void)viewWillAppear:(BOOL)animated {
if ([notes.data length]==0){
[storedText removeLastObject];
}
[self.tableView reloadData];
}
data is the NSString and storedText is the NSMutableArray. This code deletes the NSString even if it's not empty. I want it to keep the string if it contains text.
You should try something like this:
- (void)viewWillAppear:(BOOL)animated {
if ([[[storedText lastObject] data] length]==0){
[storedText removeLastObject];
}
[self.tableView reloadData];
}
BTW, it seems that your hypothesis that notes.data is the same string as the last object in storedText is not correct. This leads me to suspect that you have other kinds of errors in your code that you should also investigate. In other words, what you can expect is that your notes.data is not correct -- indeed, you should at least "update" it after you remove the last object from the array:
- (void)viewWillAppear:(BOOL)animated {
if ([[[storedText lastObject] data] length]==0){
[storedText removeLastObject];
notes = [storedText lastObject]; //-- this will be the *new* last object after removal
}
[self.tableView reloadData];
}
but I have no clue what you do with notes.data, so I do not know if this by itself is enough to bring it back to being consistent with your hypothesis.
Ideally before you add any item to storedText you would check that it wasn't nil or an empty string, then you wouldn't have the problem.
Otherwise, get the last item from storedText and check it (using isEqualToString: or a length check) and then remove it if it matches.
Follow what Wain said. Do this.
//total array size
int count = [storedText count];
int lastItemIndexInt = count - 1;
//get last object in array which is a string
NSString *str1 = [storedText objectAtIndex:lastItemIndexInt];
if ([str1 isEqualToString:#""] || [str1 length] < 1)
{
//string is null / blank, remove it
[storedText removeObjectAtIndex:lastItemIndexInt];
}
I get a double free error when using [nsdictionary enumerateKeysAndObjectsUsingBlock:]
CnFExhibition_0821(74624,0x114853000) malloc: * error for object 0x7fe972814fa0: double free
This happen mostly when using appendFormat: in enumeration block, not always happen but quite often.
I finally prevent it by not using enumerateKeysAndObjectsUsingBlock:, but still wondering why?
This happen when calling this line, which "newData.list[0]" is a NSDictionary,
[database updateRow:#"01" inTable:#"Exhibition" setting:newData.list[0] error:nil];
SQLiteHelper.m
-(BOOL)updateRow:(id)rowID inTable:(NSString*)tablename setting:(NSDictionary*)setting error:(NSError *__autoreleasing *)err{
if ([self checkTableName:tablename error:err]){
if ([self checkUpdateSetting:setting error:err]) {
NSMutableString * updateCmd = [sqlCmdUpdateFromTable(tablename) mutableCopy];
[updateCmd appendString:sqlCmdSetRow(setting)];
if (rowID) {
[updateCmd appendString:sqlCmdWhereCondition(#{[self pkOfTable:tablename]:rowID})];
}
return [self execCmdStr:updateCmd error:err];
}else{
return NO;
}
}else{
return NO;
}
}
NSString * sqlCmdSetRow(NSDictionary*setting){
if (setting && setting.count){
NSMutableString * setCmd = [NSMutableString stringWithString: #" SET "];
[[setting copy] enumerateKeysAndObjectsWithOptions:NSEnumerationConcurrent usingBlock:^(id key, id obj, BOOL *stop){
if ([obj isKindOfClass:[NSString class]]){
//*Mostly crush at this line*
[setCmd appendFormat:#"%#='%#', ",key,obj]];
}
else{
[setCmd appendFormat:#"%#=%#, ",key,obj];
}
}];
[setCmd deleteCharactersInRange:NSMakeRange(setCmd.length-2, 2)];
return setCmd;
}
else{
return nil;
}
}
Replacing enumeration in "sqlCmdSetRow" with code below and never happen again
NSArray * a = [setting allKeys];
for (NSString * s in a) {
if ([setting[s] isKindOfClass:[NSString class]]){
[setCmd appendString:[NSString stringWithFormat:#"%#='%#', ",s,setting[s]]];
}else{
[setCmd appendFormat:#"%#=%#, ",s,setting[s]];
}
}
By using -[NSDictionary enumerateKeysAndObjectsWithOptions:usingBlock: with the NSEnumerationConcurrent option, you are effectively calling appendString: and appendFormat: on the same NSMutableString object (setCmd) on multiple threads simultaneously. The documentation of those methods doesn't say anything about thread safety, so they probably aren't thread-safe. Your random crashes back that up.
You did the right thing by changing to a for-in loop. Now that you are only touching setCmd on a single thread, there is no thread safety issue and the crashes went away.