I have a quick question about member variables in a class. Is there a
way to use an NSMutableString in a class as a member? I would like to
make a string which accumulates equation text, in a calculator class. I
have tried a number of methods to get this working with no success. The
output of the NSMutableString is always Nil as is the NSString, I know
there is an issue with initialization of the strings but I can not
figure out how or why I cannot initialize them in this fashion. When
using the member function and declaring the variable locally in that
function there is no problem. Now I could pass out the Strings and
handle the concatenation in my main() but I want to keep the data in
the class and not in main. Can anyone shed some insight into why this is
not working? Comments included in the code show where I have attempted
initialization and when possible the exceptions created by the code.
This is what I currently have
<code>
#import <Foundation/Foundation.h>
@interface Calculator : NSObject
{
double accumulator;
NSMutableString *equation;
//NSMutableString equation; //= [[NSMutableString alloc]
initWithString:@"Starting Value - "];
NSString *equationI;
}
- (id)init;
-(void) dealloc;
- (void) initialize;
- (void) clear;
- (void) total;
- (void) destroy;
- (double) accumulator;
- (void) add: (double) n;
- (void) subtract: (double) n;
- (void) multiply: (double) n;
- (void) divide: (double) n;
- (void) exponent: (double) n;
@end
@implementation Calculator
- (id) init
{
[super init];
//equation = [[NSMutableString alloc] init]; //does not work
//NSMutableString *equation = [[NSMutableString alloc] init];
//causes exception, compiler says variable is not used.
return self;
}
- (void)dealloc
{
//[myNewString release];
[equation release];
[equationI release];
//[super dealloc]; // pointer being freed was not allocated
}
- (void) initialize
{
accumulator = 0;
/*Some things i have tried */
//equation = "Init";
//NSMutableString equation = [[NSMutableString alloc] init];
//NSMutableString *equation = [*equation appendString:"Init"];
//NSMutableString *equationI = "Init2";
//NSMutableString equation = [[NSMutableString alloc]
initWithString:@"Init"];
//equation = [[NSMutableString alloc] initWithString:@"Test 002"];
//causes a crash
//equation = [[NSMutableString alloc] initWithString:@"s"]; //causes
exception
//equationI = [[NSString alloc] init];
equation = [equation initWithString:@"test"];
equationI = [equationI initWithString:@"test2"];
//[equation setString:@"test1"];
//[equationI setString:@"test2"];
NSLog(@"%@ \n", equation);
NSLog(@"%@ \n", equationI);
[equation appendString:@"Initialized"];
//equation = @"Equation - ";
//[equation setString: @"Equation:"];
//[equationI appendFormat: @"%f", accumulator ];
[equation stringByAppendingFormat: @"Equation - %f", accumulator ];
}
- (void) clear
{
}
- (void) total
{
NSLog(@"Displaying NSMutableString %@ = %f", equation, accumulator);
NSLog(@"Displaying NSString %@ = %f", equationI, accumulator);
}
- (void) destroy
{
}
- (double) accumulator
{
return accumulator;
}
- (void) add: (double) n
{
accumulator += n;
[equation appendFormat: @" + %f ", n];
NSString* myNewString = [NSString stringWithFormat:@"%f", n];
NSLog(@"%@", myNewString);
[equation stringByAppendingFormat: @" + %f ", n];
}
- (void) subtract: (double) n
{
accumulator -= n;
[equation appendFormat: @" - %f ", n];
NSString* myNewString = [NSString stringWithFormat:@"%f", n];
NSLog(@"%@", myNewString);
[equation stringByAppendingFormat: @" - %f ", n];
}
- (void) multiply: (double) n
{
accumulator *= n;
[equation appendFormat: @" * %f ", n];
NSString* myNewString = [NSString stringWithFormat:@"%f", n];
NSLog(@"%@", myNewString);
[equation stringByAppendingFormat: @" * %f ", n];
}
- (void) divide: (double) n
{
accumulator /= n;
[equation appendFormat: @" %f / %f ", n];
NSString* myNewString = [NSString stringWithFormat:@"%f", n];
NSLog(@"%@", myNewString);
[equation stringByAppendingFormat: @" / %f ", n];
}
- (void) exponent: (double) n
{
accumulator = pow(accumulator, n);
[equation appendFormat: @" ^ %f ", n];
NSString* myNewString = [NSString stringWithFormat:@"%f", n];
NSLog(@"%@", myNewString);
[equation stringByAppendingFormat: @" ^ %f ", n];
}
@end
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
// insert code here...
Calculator *deskCalc = [[Calculator alloc] init];
[deskCalc init];
[deskCalc initialize];
[deskCalc add:10];
[deskCalc subtract:5];
[deskCalc total];
[deskCalc dealloc];
[deskCalc release];
NSLog(@"Hello, World!");
[pool drain];
return 0;
}
</code>
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