CODEWITHSUNDEEP
iosobjective-cintlong-integermultiplication
user1833903
user1833903

Reputation: 197

Multiplication doesn't give the right answer

I'm working with multiplications in my objective c application. The problem is, when i do some multiplications, sometimes it gives me a false result :

Exemple :

int intern = 77986;
int secondNumber = 70654;
long long int multiply = intern * secondNumber;
NSLog(@"Intern : %i   two : %i   mult : %lli", intern, secondNumber, multiply);

The result is :

Intern : 77986 two : 70654 mult : 1215055548

The result would be 5510022844

I don't understand... Thank you for your help !

Upvotes: 0

Views: 114

Answers (2)

rmaddy
rmaddy

Reputation: 318804

It's a simple overflow issue. An operation with two int variables is done as an int. But the result is too big for int so it overflows. Then the overflowed result is assigned to the long long int.

Making either (or both) of the first two int variables into long long int will result in the operation being done as a long long int resulting in the expected and correct result.

To clarify, you can either do:

long long int intern = 77986;
// and the rest

or do:

long long int multiply = (long long int)intern * secondNumber;

Upvotes: 3

Marc B
Marc B

Reputation: 360662

 125055548 -> 0x 486C46BC
5510022844 -> 0x1486C46BC

Since you're multiplying ints, the result is an int, and gets truncated down to 32bits.

Upvotes: 0

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