coding in C : Task $2$: String to number

In this task, you will ask the user for a string $x$ that represents a real number and the base $b$ in which this number is given. Your task is to convert this string in to the floating number in base $10.$

Note. Number in base $10$ are the numbers we use in our daily basis were all the number's digits are less than $10.$

Example:

$x=75\mathrm{.}32,b=8,$ Output: $61\mathrm{.}40625$

Explanation:

$-7*8^1=56$

$-5*8^0=5$

$-3*8^{-1}=0\mathrm{.}375$

$-2*8^{-2}=0\mathrm{.}03125$

$-3*8^{-1}=0\mathrm{.}375$

$-2*8^{-2}=0\mathrm{.}03125$

Output: $56+5+0\mathrm{.}375+0\mathrm{.}03125=61\mathrm{.}40625$

$x=-75\mathrm{.}32,b=8,$ Output: $-61\mathrm{.}40625$