Convert to Float and Calculate

Question

I have a line with several numbers and operators

@ "5+4-9/10" .

How to get the result from it?

I want to use it in the calculator that I use. I will have to dynamically display the result when I press a number or operator.

I used the arity arar file in android . But I can not achieve something like this in the iPhone .

Answer 1

How about this -

 NSString *formula = @"1+5*6"; NSExpression *exp = [NSExpression expressionWithFormat:formula]; NSNumber *resultForCustomFormula = [exp expressionValueWithObject:nil context:nil]; NSLog(@"%f", [resultForCustomFormula floatValue]); 

EDIT: Now I thought about your requirement and made a method using NSScanner . You won’t believe that I didn’t use NSScanner until Mr. Borrrden suggested I use it, and I found it wonderful. See below method -

 -(NSMutableString *)formatString:(NSString *)formula { // Let check if there any wrong (.) value exm: 1/.2 or .7+3 // 1/0.2 and 0.7+3 are okay but above are incorrect so first fix them NSString *str = formula; NSInteger c = 0; for(int i=0; i<[str length]; i++) { if([[NSString stringWithFormat:@"%c",[str characterAtIndex:i]] isEqualToString:@"+"] || [[NSString stringWithFormat:@"%c",[str characterAtIndex:i]] isEqualToString:@"-"] || [[NSString stringWithFormat:@"%c",[str characterAtIndex:i]] isEqualToString:@"/"] || [[NSString stringWithFormat:@"%c",[str characterAtIndex:i]] isEqualToString:@"*"]) { if([str length] > i+1) { if([[NSString stringWithFormat:@"%c",[str characterAtIndex:i+1]] isEqualToString:@"."]) { formula = [formula stringByReplacingCharactersInRange:NSMakeRange(i+1+c, 1) withString:@"0."]; c++; } } } } // Now we will convert all numbers in float NSString *aString; float aFloat; NSMutableString *formattedString = [[NSMutableString alloc]init]; NSScanner *theScanner = [NSScanner scannerWithString:formula]; while ([theScanner isAtEnd] == NO) { if([theScanner scanFloat:&aFloat]) { [formattedString appendString:[NSString stringWithFormat:@"%f",aFloat]]; } if([theScanner scanUpToCharactersFromSet:[NSCharacterSet decimalDigitCharacterSet] intoString:&aString]) { [formattedString appendString:aString]; } } return formattedString; } 

This will convert (2.222 / .4) + 9999-7 + 0.7 * .13 to (2.222000 / 0.400000) + 9999.000000-7.000000 + 0.700000 * 0.130000 .
Just call this method before using NSExpression .

 NSString *formula = @"(2.222/.4)+9999-7+0.7*.13"; NSString *formattedString = [self formatString:formula]; NSExpression *exp = [NSExpression expressionWithFormat:formattedString]; NSNumber *resultForCustomFormula = [exp expressionValueWithObject:nil context:nil]; NSLog(@"Result = %f", [resultForCustomFormula floatValue]); //OutPut: Result = 9997.646484 

Note. I am not saying that it will work on all lines of the formula. Maybe in some case this will not work. But he will work in general equations.

Answer 2

Note that : You need to pass at least one floating point value .

I know this is not the best way, but something like this may work for you.

 NSString *formula = @"5+4-9/10"; NSString *str = [formula lastPathComponent]; formula = [formula stringByReplacingOccurrencesOfString:str withString:[NSString stringWithFormat:@"%@.0",str]]; NSString *strCal=[NSString stringWithString:formula]; NSExpression *exp=[NSExpression expressionWithFormat:strCal]; float result=[[exp expressionValueWithObject:nil context:nil] floatValue]; NSLog(@"result:%f",result); 

You can use GCMathParser or DDMathParser .

I do not know if this is the most effective method or not, but I wrote to help you anyway ... !!!

Answer 3

You can parse "all" numbers for swimming:

 NSMutableString *numericExpression = [NSMutableString stringWithString:@"4+3/2-7/4"]; NSMutableString *nExp=[NSMutableString stringWithString:@""]; BOOL innum=false; BOOL dotfound=false; for (NSInteger charIdx=0; charIdx<numericExpression.length; charIdx++){ NSString *substr=[NSString stringWithFormat:@"%C",[numericExpression characterAtIndex:charIdx]]; if (isdigit([numericExpression characterAtIndex:charIdx])) { // in number innum=true; }else if ([substr isEqualToString:@"."]){ // dot found ... innum=true; dotfound=true; }else{ // not in number if (innum && dotfound) { NSLog(@"all good (*).*"); }else if(innum && !dotfound){ NSLog(@"adding .0"); [nExp appendString:@".0"]; } innum=false; dotfound=false; } [nExp appendString:substr]; NSLog(@"%@",nExp); } NSExpression *expression = [NSExpression expressionWithFormat:nExp]; NSNumber *result = [expression expressionValueWithObject:nil context:nil]; NSLog(@"calc %@ = %@",nExp,result);