Exercise $3($convert char digits into int $)$

Write a function that accepts a character array representing digits of an unsigned integer with its digits stored in the reversed order and returns the integer value represented by these characters. For example, the function convertInt when called on the array char a$[]=\{\text{'}3\text{'},\text{'}2\text{'},\text{'}1\text{'}\}$ would return integer value $123.$ Parameter n holds the number of digits stored in the array.