Question: I have to read from standard input two numbers as strings, in C. How can I print their sum as a string too? I have:

```
char a[10],b[10];
printf("enter the two numbers");
scanf("%s%s",&a,&b);
char sum[20];
sum=?

```

A little tip,please?
Thank you!

Answer: 
Do this with programming just as you would do it on paper. Make small steps, and make explicit every little step that we do on paper without noticing.

```
    00111
 ---------
     12345
 123456789
 ---------
 123469134

```

* Notice different lengths. You'll need separate vars to hold that info. You'll need to find out the two lengths - either use a standard function, or write your own: strings end with a binary `0`.
* Notice how we go backwards while we add. You'll have to maintain two indices to access the two strings (arrays of chars).
* Notice how we carry over the high digit of the addition `5+9=14`. You'll need to maintain that in another variable.

Use loops. After you've added, you will need to know the total length, and move it to the left edge. Because we don't know in advance what length we'll get, you'll start writing down the answer from the right edge of your `sum` array. Think, how and what can you improve about this.
Convert the strings into numbers using `atoi`, then add them together, and then print the sum using a print function like printf. See [this](http://www.cplusplus.com/reference/cstdlib/atoi/)