I was first making a big answer with a large code into the back-memory, but finally I made that :
1'(`>0.>{@}0'{v}1'0,>48-0,-<~>$>$
Here is an explanation :
1' // Go to the second cell, the first will be used to store an information
( // Input a string
` // Go to the last cell (at the last character of the string)
> // Make a new cell after the string
0. // Store a 0 to mark the end of the string
> // Make a new cell
{@} // Store this adress into the back-memory
0' // Go to the 1st cell
{v} // Paste the adress, now the 1st cell contains the adress which points after the '0' which marks the end of the string
1' // Go to the 2nd cell (the beginning of the string)
0, // While we do NOT encounter a zero (while the string is not terminated)
> // Go to the next cell (the repeat number)
48- // Substract 48 to get the number (the string was stored as an ASCII chain)
0, // While this cell is not equal to 0 (higher than 0)
- // Decrease the cell
< // Go to the cell which contains the character to repeat
~ // Display it
> // Go to the number
$ // End of the loop
> // Go to the next number
$ // End of the loop
So we make a loop across the string, and a second loop into which display the C
character `` times.