complement.c

#include <ctype.h>
#include <stdio.h>

int main(int argc, char **argv)
{
        char line[8192];
        char *j, c;
        while (fgets(line, sizeof(line), stdin)) {
                if (line[0] == '>') {
                        printf("%s", line);
                        continue;
                }

                for (j = line; *j; j++) {
                        switch (toupper(*j)) {
                        case 'A':
                                c = 'T';
                                break;
                        case 'C':
                                c = 'G';
                                break;
                        case 'G':
                                c = 'C';
                                break;
                        case 'T':
                        case 'U':
                                c = 'A';
                                break;
                        case 'M':
                                c = 'K';
                                break;
                        case 'R':
                                c = 'Y';
                                break;
                        case 'W':
                                c = 'W';
                                break;
                        case 'S':
                                c = 'S';
                                break;
                        case 'Y':
                                c = 'R';
                                break;
                        case 'K':
                                c = 'M';
                                break;
                        case 'V':
                                c = 'B';
                                break;
                        case 'H':
                                c = 'D';
                                break;
                        case 'D':
                                c = 'H';
                                break;
                        case 'B':
                                c = 'V';
                                break;
                        case 'N':
                                c = 'N';
                                break;
                        default:
                                c = *j;
                        }

                        printf("%c", c);
                }
        }
}