Will this help you;
int nNumber = 0;
// Convert the string to number.
nNumber = atoi(szTemp);
printf("The converted number is : %d \n",nNumber);
Also I've found this
site while searching a little,it has some nice things.Anyway you could search yourself a little,because there are so many guides,tutorials and books about C on the net that will help you understand C much better and we have Programming forum here,so you could've started your thread there and searched it a little too.