#### If you are familiar with array and string, feel free to skip to STEP 3. 

#### STEP 1: Read the following function to understand the basics of array


```c
int sum_of_array()
{
  int array[10]; //This is how you declare an int array
  //Initialize the array as 0,...,9
  for(int i = 0; i < 10;i++){
    array[i] = i; 
  }
  int sum = 0;
  for(int i = 0; i < 10;i++){
    sum += array[i]; //same as sum = sum + array[i]
  }
  return sum;
}
```

#### STEP 2: Read the following function to understand how string is implemented using array of char

```c
int my_first_string()
{
  char my_string[13]; //Declear an array of char with size 12
  my_string[0] = 'I'; //Using single quote to denote a char
  my_string[1] = ' '; //This is a space
  my_string[2] = 'a';
  my_string[3] = 'm';
  my_string[4] = ' ';
  my_string[5] = 's';
  my_string[6] = 't';
  my_string[7] = 'r';
  my_string[8] = 'i';
  my_string[9] = 'n';
  my_string[10] = 'g';
  my_string[11] = '\n'; //This is a new line symbol;
  my_string[12] = '\0'; // THIS IS VERY VERY VERY IMPORTANT. In C, we have to put a backslash zero to indicate the end of a string.

  printf("%s",my_string); //This will print the string including the new line.
  return 0;
}
```

#### STEP 3: Complete the following function to create a string which prints all 26 letters in upper case and lower case alternatively. 

#####The desired output shoud be `AaBbCcDdEeFfGg....Zz`
Hints:

* Do it in a loop.