NSDecimalNumber *d1 = [NSDecimalNumber decimalNumberWithString:@"3.14"];

    NSDecimalNumber *d2 = [NSDecimalNumber decimalNumberWithString:@"2"];

    NSDecimalNumber *s = [d1 decimalNumberByAdding:d2];

    NSLog(@"s = %@",s);

    s = [d1 decimalNumberBySubtracting:d2];

    NSLog(@"s = %@",s);

    s = [d1 decimalNumberByMultiplyingBy:d2];

    NSLog(@"s = %@",s);

    s = [d1 decimalNumberByDividingBy:d2];

    NSLog(@"s = %@",s);

iOS 数字字符串的直接运算 + - * /