Question

Given the string:

"10 + 20 - 5 * 7 + (20 / 5)"

Are there any parsers available that could evaluate this, or would I need to write my own?

Answer 1

Take a look at this post by newacct.

NSString *equation = @"10 + 20 - 5 * 7 + (20 / 5)";

// dummy predicate that contains our expression
NSPredicate *pred = [NSPredicate predicateWithFormat:
                      [equation stringByAppendingString:@" == 42"]];//42 is just a rightExpression to make it an equation
NSExpression *exp = [pred leftExpression];
NSNumber *result = [(NSComparisonPredicate *)exp expressionValueWithObject:nil context:nil];
NSLog(@"%@", result); // logs "-1"