The header <stdlib.h> declares functions for number conversion, storage allocation, and similar tasks.
double atof(const char *s)
atof converts s to double; it is equivalent to strtod(s, (char**)NULL).
int atoi(const char *s)
converts s to int; it is equivalent to (int)strtol(s, (char**)NULL, 10).
long atol(const char *s)
converts s to long; it is equivalent to strtol(s, (char**)NULL, 10).
