Search for errors in the code

In the following tasks, some programmer has written code and maybe have made errors in it. You should check if the code perform what it is described. If the code does not work correctly, you need to fix the errors.

Задание 1

The code should find the sum of numbers:

javascriptlet num1 = 1;
let num2 = 2;
console.log('Sum: ' + num1 + num2);
Задание 2

The code should find the sum of numbers:

javascriptlet a = 1;
let b = 2;
console.log(a + b + c);
Задание 3

The code should find the sum of the digits of the number:

javascriptlet num = '123';
let sum = num[0] + num[1] + num[2];
console.log(sum);
Задание 4

The code should output the first digit of the number:

javascriptlet num = 123;
console.log(num[0]);
Задание 5

The code was supposed to print the number 1 to the console, but it prints 0:

javascriptlet a = 0;
console.log(a++);
Задание 6

The code should output the number of digits in the number:

javascriptlet num = 123;
console.log(num.length);
Задание 7

The code should obtain the number of seconds in a day:

javascriptlet a = 24 / 60 / 60;
console.log(a);
Задание 8

The code should output the number of digits in the number:

javascriptlet num = 123;
let str = String(num);
console.log(num.length);
Задание 9

The code should output the last digit of the number:

javascriptlet num = 123;
let str = String(num);
console.log(num[num.length]);
Задание 10

The code should output the number of digits in the number:

javascriptlet num = 123;
let str = String(num);
console.log(str.lenght);
Задание 11

The code should output the last digit of the number:

javascriptlet num = 123;
let str = String(num);
console.log(str[str.length]);
Задание 12

The code should find the sum of the numbers:

javascriptlet a = '123';
let b = '456';
let s = Number(a) + String(b);

console.log(s);