atoi - convert ascii to integer
Standard C Library (libc, -lc)
atoi(const char *string);
string, which should be a textual representation of an integer, is converted to the machine representation of that integer. Leading whitespace, if any, is skipped. Conversion stops when a non-numeric character is found.
atoi returns the number converted. If no digits at all were found, it returns 0. If too many digits are found (resulting in overflow) the behavior is formally undefined.