How to evaluate the string equation in ios

StackOverflow https://stackoverflow.com/questions/16785873

Question

Is there way to solve the string equations in ios ?

For example

Input:

NSString * str =@"1+2";

Output:

NSInteger result = 3 // i.e sum of 1+2 from str

How to go about this and get expected result!

Please help!

Was it helpful?

Solution

You can use NSExpression for this:

NSExpression *expression = [NSExpression expressionWithFormat:@"1+2"];
NSLog(@"%@", [expression expressionValueWithObject:nil context:nil]);

For further information read the documentation of the used methods.

OTHER TIPS

If your mathematical expressions are simple enough, you could go the manual route as suggested by Rajan Balana.

To evaluate more complex expressions, you could use/abuse NSPredicate in combination with NSExpression as described in this Blog post:http://funwithobjc.tumblr.com/post/1553469975/abusing-nspredicate

Note that NSPredicate is only necessary if your input is really an equation (including the right part):

NSPredicate* parsedExpression = [NSPredicate predicateWithFormat:@"1+2=x"];
NSExpression* leftPart = [(NSComparisonPredicate*)parsedExpression leftExpression];
NSNumber* evaluatedResult = [leftPart expressionValueWithObject:nil context:nil];
NSLog(@"Expr:%@", evaluatedResult);

To achieve proper parsing, you can use one of the math parsers for Objective-C out there. I haven't used them myself, but the popular ones seem to be

Use this :

NSString * str =@"1+2";

NSArray *arr = [str componentsSeparatedByString:@"+"];
int sum = 0;
for (int i = 0; i < [arr count]; i++) {
    sum += [[arr objectAtIndex:i] intValue];
}
NSLog(@"sum : %d",sum);

Output : sum = 6

You can use NSExpression also.

Expressions are the core of the predicate implementation. When expressionValueWithObject: is called, the expression is evaluated, and a value returned which can then be handled by an operator. Expressions can be anything from constants to method invocations. Scalars should be wrapped in appropriate NSValue classes.

Example :

    NSLog(@"sum : %@", [[NSExpression expressionWithFormat:@"1+4"] expressionValueWithObject:nil context:nil]);
Output :- sum : 5
    NSLog(@"mulitple : %@", [[NSExpression expressionWithFormat:@"2*4"] expressionValueWithObject:nil context:nil]);
Output :- mulitple : 8

Hope it helps you.

What you can do is, You can get the components of the string separated by the sign "+" using this method and then you will get the array of components i.e. 1,2.

NSArray* foo = [str componentsSeparatedByString: @"+"];

int result = [[foo objectAtIndex:0] integerValue] + [[foo objectAtIndex:1] integerValue];

and then you can use the integer value for those two elements and add them and store the result in an integer variable.

I think you need to subString your string, and store each number in a new NSstring(integerValue) or in Integer variable.

example:

NSString *str = @"1+2";
    int x = [[str substringToIndex:1]integerValue];
    int y = [[str substringFromIndex:1]integerValue];
    int z = x+y;
    NSLog(@"Sum === %d",z);

Depends on complexity of your input string equations. You can use Shunting-yard algorithm for parsing mathematical equations and then calculate the equation from the Abstract Syntact Tree (AST)

But I expect you are looking for some easy, preferably already done solution. In that case you can take a try one of these (no guarantee, I haven't tried those, just googled):

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