Do it in C please, without using parseint, atoi.

* The isinteger ) function examines the string given as its first argument, and returns true if and only if the string represents a well-formed integer. A well-formed integer consists only of an optional leading - followed by one or more decimal digits. Returns true if the given string represents an integer, false otherwise. bool isinteger (char +str) *The parseint ) function parses a well-formed string representation of * an integer (one which would return true from isinteger )) and returns the integer value represented by the string. For example, the string "1234" would return the value 1234 This function does not need to handle badly-formed strings in any partichacular fashion, its operation on badly-formed strings is undefined. Returns the integer value stored in the given string. int parseint (char str)i