In addition, the digits of the same number should be aligned, and the next digit should be calculated after calculating one digit.

When the sum reaches 10, the first digit reaches 1. When adding, the last digit reaches 10, which is recorded as "0", and the next digit is added with 1.

The calculation order is from small to large, one, ten, and one hundred. Addition operation is a basic operation method in mathematical calculation. Addition is to add two numbers and calculate the sum of these two numbers.