/* lots of functions for summing the first n integers */

#include <stdio.h>
#include <stdlib.h> /* for atoi */

int sum1(int n) { 
  return ((n+1)*n) / 2;
}

int sum2(int n) {
  if(n==0) {
    return 0;
  } else {
    return sum2(n-1) + n;
  }
}

int sum3(int n) {
  if(n==0)
    return 0;
  return sum3(n-1) + n;
}

int sum4(int n) {
  int ans = 0;
  while(n != 0) {
    ans += n;
    n -= 1;
  }
  return ans;
}

int sum5(int n) {
  int ans = 0;
  while(n) {
    ans += n;
    --n; /* or n-- or n = n - 1 */
  }
  return ans;
}

int sum6(int n) {
  int ans = 0;
  while(n)
    ans += n--; /* NOT --n */
  return ans;
}

int sum7(int n) {
  int ans = 0;
  for(; n >= 0; --n) {
    ans += n;
  }
  return ans;
}

int sum8(int n) {
  int ans = 0;
  for(; n >= 0; ans+=n, --n) 
    ;
  return ans;
}

int sum9(int n) {
  int ans = 0;
  while(1) {
    if(n==0)
      break;
    ans += n--;
  }
  return ans;
}

int sum10(int n) {
  int ans = 0;
  while(1) {
    if(n==0)
      return ans;
    ans += n--;
  }
}
    
int sum11(int n) {
  int ans = 0;
  goto L2;
 L1: return ans;
 L2:
  if(n==0)
    goto L1;
  ans += n--;
  goto L2;
}

int sumWrong(int n) {
  /* illegal because of goto into scope */
  if(n==0)
    return 0;
  goto L2;
  {int ans = 0;
 L1: return ans;
 L2:
  if(n==0)
    goto L1;
  ans += n--;
  goto L2;
  }
}

int main(int argc, char**argv) {
  if(argc != 2) {
    fprintf(stderr,"bad args");
    return 1;
  }
  { int num = atoi(argv[1]);
  if(num < 0) {
    fprintf(stderr,"bad args");
    return 1;
  }
  /* later we will use function pointers to avoid this copy/paste */
  fprintf(stdout, "1: %d\n", sum1(num));
  fprintf(stdout, "2: %d\n", sum2(num));
  fprintf(stdout, "3: %d\n", sum3(num));
  fprintf(stdout, "4: %d\n", sum4(num));
  fprintf(stdout, "5: %d\n", sum5(num));
  fprintf(stdout, "6: %d\n", sum6(num));
  fprintf(stdout, "7: %d\n", sum7(num));
  fprintf(stdout, "8: %d\n", sum8(num));
  fprintf(stdout, "9: %d\n", sum9(num));
  fprintf(stdout, "10: %d\n", sum10(num));
  fprintf(stdout, "11: %d\n", sum11(num));
  fprintf(stdout, "11: %d\n", sumWrong(num));
  }
  return 0;
}