Something

#include <stdio.h>

int main(void)
{
  int c;
  while ((c = getchar()) != EOF) {
    if (c > 33 && c < 58) {
      c = c + 32;
      printf("The character is %c \n",c);
    } else if (c < 90 && c > 65) {
      c = c - 32;
      printf("The character is %c \n",c);
    } else {
      printf(" Incorrect input\n");
    }
  }
  return 0;
}