atoll - Converts string into long long integer value in C

  #include <stdlib.h>
  #include <stdio.h>

  int main(void)
  {
    char num1[80], num2[80];

    printf("Enter first: ");
    gets(num1);
    printf("Enter second: ");
    gets(num2);
    printf("The sum is: %ld.", atoll(num1)+atoll(num2));

    return 0;
  }

Output:
Enter first: 3
Enter second: 3
The sum is: 6.