#include <stdio.h>
#include <string.h>

int main(int argc, char **argv)
{
    int dflag, c;

    if (argc != 3) {
        fprintf(stderr, "usage: %s {fromchar tochar | -d delchar}\n", argv[0]);
        return(1);
    }
    dflag = (strcmp(argv[1], "-d") == 0);
    if ((!dflag && strlen(argv[1]) != 1) || strlen(argv[2]) != 1) {
        fprintf(stderr, "%s: argument must be a single character\n", argv[0]);
        return(1);
    }
    if (dflag) {
        while ((c = getchar()) != EOF)
            if (c != argv[2][0])
                putchar(c);
    } else {
        while ((c = getchar()) != EOF)
            if (c == argv[1][0])
                putchar(argv[2][0]);
            else
                putchar(c);
    }
    return(0);
}