String to Integer
int atoi(char s[])
{
int n = 0;
for (int i = 0; s[i] >= '0' && s[i] <= '9'; i++)
n = 10*n + (s[i] - '0');
return n;
}
int atoi(char s[])
{
int n = 0;
for (int i = 0; s[i] >= '0' && s[i] <= '9'; i++)
n = 10*n + (s[i] - '0');
return n;
}