please answer in C

7. negate_armstrongs: Takes an array of integers and the length of the array as input and negates every element of the array that is an An Armstrong number (also called a Narcissistic number) is a number that is equal to the sum of its digits each raised to the power of the number of digits. For example, 153 is an Armstrong number because it has 3 digits and 13+53+33=153. Thus, if an input array contains [2, 153,153], then after a call to negate_armstrongs the array will contain [2, 153,153]