caesar cypher .c

caesar.c

#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[]) {
  if (argc <= 1) {
    printf("Usage: %s [+/-shift]\n", argv[0]);
    return 1;
  }
  char* shift_str = argv[1];
  int sign = 1;
  if (shift_str[0] == '-') {
    sign = -1;
    shift_str++;
  } else if (shift_str[0] == '+') {
    shift_str++;
  }
  int shift = atoi(shift_str);
  shift *= sign;
  FILE* stdin = fopen("/dev/stdin", "r");
  while (!feof(stdin)) {
    char c = fgetc(stdin);
    if (c == EOF) {
      break;
    }
    if (c == '\n') {
      printf("\n");
      continue;
    }
    printf("%c", (c+shift)%256);
  }
}