do_my_science_homework.c

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

char last_input;

char *getstdin() {
    char *line = NULL, *tmp = NULL;
    size_t size = 0, index = 0;
    int ch = EOF;

    while (ch) {
        ch = getc(stdin);

        /* Check if we need to stop. */
        switch (ch) {
            case EOF:
                last_input = 1;
            case '\n':
                ch = 0;
                break;
        }

        /* Check if we need to expand. */
        if (size <= index) {
            size += 1;
            tmp = realloc(line, size);
            if (!tmp) {
                free(line);
                line = NULL;
                break;
            }
            line = tmp;
        }

        /* Actually store the thing. */
        line[index++] = ch;
    }

    return line;
}

char *dna_anticodon(char *dna) {
    size_t bufsize = strlen(dna)/3*4 + 1;
    char *anticodons = malloc(sizeof(char) * bufsize);
    memset(anticodons, 0, bufsize);
    char *p = dna;
    char *np = anticodons;
    char a = 0;
    while (*p) {
        if (*p == 'T') *np = 'U';
        else *np = *p;
        p++;
        np++;
        if (++a == 3) {
            *np = '-';
            np++;
            a = 0;
        }
    }
    return anticodons;
}

char *dna_mrna(char *dna) {
    size_t bufsize = strlen(dna)/3*4 + 1;
    char *mrna = malloc(sizeof(char) * bufsize);
    memset(mrna, 0, bufsize);
    char *p = dna;
    char *np = mrna;
    char a = 0;
    while (*p) {
        switch (*p) {
            case 'A':
                *np = 'U';
                break;
            case 'T':
                *np = 'A';
                break;
            case 'C':
                *np = 'G';
                break;
            case 'G':
                *np = 'C';
                break;
        }
        p++;
        np++;
        if (++a == 3) {
            *np = '-';
            np++;
            a = 0;
        }
    }

    return mrna;
}

char *mrna_aa(char *mrna) {
    size_t mrna_len = strlen(mrna);
    mrna[mrna_len-mrna_len%4+1] = 0;
    size_t bufsize = strlen(mrna) + 1;
    char *aa = malloc(sizeof(char) * bufsize);
    memset(aa, 0, bufsize);
    char *p = mrna;
    char *aap = aa;
    while (*p) {
        switch (*p) {
            case 'A':
                switch (1[p]) {
                    case 'A':
                        switch (2[p]) {
                            case 'A':
                            case 'G':
                                strcpy(aap, "Lys ");
                                aap += 4;
                                break;
                            default:
                                strcpy(aap, "Asn ");
                                aap += 4;
                                break;
                        }
                        break;
                    case 'C':
                        strcpy(aap, "Thr ");
                        aap += 4;
                        break;
                    case 'G':
                        switch (2[p]) {
                            case 'A':
                            case 'G':
                                strcpy(aap, "Arg ");
                                aap += 4;
                                break;
                            default:
                                strcpy(aap, "Ser ");
                                aap += 4;
                                break;
                        }
                        break;
                    case 'U':
                        switch (2[p]) {
                            case 'G':
                                strcpy(aap, "Met ");
                                aap += 4;
                                break;
                            default:
                                strcpy(aap, "Ile ");
                                aap += 4;
                                break;
                        }
                        break;
                }
                break;
            case 'C':
                switch (1[p]) {
                    case 'A':
                        switch (2[p]) {
                            case 'A':
                            case 'G':
                                strcpy(aap, "Gln ");
                                aap += 4;
                                break;
                            default:
                                strcpy(aap, "His ");
                                aap += 4;
                                break;
                        }
                        break;
                    case 'C':
                        strcpy(aap, "Ser ");
                        aap += 4;
                        break;
                    case 'G':
                        strcpy(aap, "Arg ");
                        aap += 4;
                        break;
                    case 'U':
                        strcpy(aap, "Leu ");
                        aap += 4;
                        break;
                }
                break;
            case 'G':
                switch (1[p]) {
                    case 'A':
                        switch (2[p]) {
                            case 'A':
                            case 'G':
                                strcpy(aap, "Glu ");
                                aap += 4;
                                break;
                            default:
                                strcpy(aap, "Asp ");
                                aap += 4;
                                break;
                        }
                        break;
                    case 'C':
                        strcpy(aap, "Ala ");
                        aap += 4;
                        break;
                    case 'G':
                        strcpy(aap, "Gly ");
                        aap += 4;
                        break;
                    case 'U':
                        strcpy(aap, "Val ");
                        aap += 4;
                        break;
                }
                break;
            case 'U':
                switch (1[p]) {
                    case 'A':
                        switch (2[p]) {
                            case 'A':
                            case 'G':
                                strcpy(aap, "Stop");
                                aap += 4;
                                break;
                            default:
                                strcpy(aap, "Tyr ");
                                aap += 4;
                                break;
                        }
                        break;
                    case 'C':
                        strcpy(aap, "Ser ");
                        aap += 4;
                        break;
                    case 'G':
                        switch (2[p]) {
                            case 'A':
                                strcpy(aap, "Stop");
                                aap += 4;
                                break;
                            case 'G':
                                strcpy(aap, "Trp ");
                                aap += 4;
                                break;
                            default:
                                strcpy(aap, "Cys ");
                                aap += 4;
                                break;
                        }
                        break;
                    case 'U':
                        switch (2[p]) {
                            case 'A':
                            case 'G':
                                strcpy(aap, "Leu ");
                                aap += 4;
                                break;
                            default:
                                strcpy(aap, "Phe ");
                                aap += 4;
                                break;
                        }
                        break;
                }
                break;
        }
        p += 4;
    }
    return aa;
}

int main() {
    for (;;) {
        char *dna = getstdin();
        if (strlen(dna) == 0 && last_input) break;
        char *mrna = dna_mrna(dna);
        printf("mRNA:        %s\n", mrna);
        char *anticodons = dna_anticodon(dna);
        char *aa = mrna_aa(mrna);
        char *tmp=mrna;
        while(*(++tmp));
        if (*(--tmp) == '-') *tmp = 0;
        tmp=anticodons;
        while(*(++tmp));
        if (*(--tmp) == '-') *tmp = 0;
        printf("Anticodons:  %s\n"
               "Amino Acids: %s\n",
               anticodons, aa);
        free(dna);
        free(mrna);
        free(anticodons);
        free(aa);
        if (last_input) break;
    }
    return 0;
}