Program: Print the electronic configuration of an element

I had not written a C program since a long long time and decided to have a go at writing one. I was so low on confidence that I first wrote the "Hello World" program and was deliriously happy when it compiled without any errors. And then fell off my chair with uncontrollable joy when it produced the expected output.

I could have stopped then and there - a happy man. But, I have a tendency to get myself in troubling situations. Somehow, I ended up deciding to write a program to print the electronic configuration of an element given its atomic number. After fighting ferociously with logical and syntactic errors, I managed to complete the program. However, I did not have the patience to handle the exceptions in 3d,4d,5d.

For example, if you enter the atomic number as 15(phosphorus), then the program prints out:
1s2 2s2 2p6 3s2 3p3

Someday, if i gather enough patience, I will modify the program to handle these exceptions. Until then, just look upon the program as a mental exercise.

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

#define AMIN 1
#define AMAX 120

int get_sub_shell_name(int snumber)
{
if(snumber<1) {
  printf("get_sub_shell_name: Invalid shell number %d", snumber);
  return -1;
}
switch(snumber) {
  case 1: return 's';
  case 2: return 'p';
  case 3: return 'd';
  case 4: return 'f';
  default: return 'f'+(snumber-4);
}
}

int get_max_electrons(int n)
{
int total = 2;
int i;
for(i=1;i<n;i++) {
  total+=4;
}
return total;
}

/* returns the number of electrons yet to be accounted for */
int print_next_diagonal(int rem, int row, int col)
{
int i = row;
int j = col;
int snumber, sname, enumber;

while(j>0 && rem>0) {
  snumber = i;
  sname = get_sub_shell_name(j);
  enumber = get_max_electrons(j);
  if(rem < enumber)
    enumber = rem;

  printf("%d", snumber);
  printf("%c", sname);
  printf("%d ", enumber);

  rem -= enumber;
  i++;
  j--;
}
return rem;
}


void print_shell_configuration(int anumber)
{
int i, j, rem, ret;

i = j = 1;
rem = anumber;
while(rem > 0) {
  while(j <= i && rem > 0) {
    rem = print_next_diagonal(rem, i, j);
    j++;
  }
  i++;
  j = i - 1;
}
}


int main()
{
int anumber;

printf("Enter the atomic number of the element:");
scanf("%d", &anumber);

if(anumber < AMIN) {
  printf("Atomic number cannot be zero or negative.\n");
  exit(1);
}

if(anumber > AMAX) {
  printf("The element does not exist. Perhaps you have found a new one.\n");
  exit(1);
}

print_shell_configuration(anumber);
printf("\n");

return 0;
}