Counting DNA Nucleotides ==> http://rosalind.info/problems/dna/

main.c

#include <stdio.h>

int main(int argc, char * argv[])
{
        if(argc < 2){
        fprintf(stderr, "Missing argument !\n");
        return -1;
        }

        if(argc > 2){
        fprintf(stderr, "Too many arguments\n");
        return -1;
        }


        unsigned i;
        unsigned a=0, t=0, c=0, g=0;

        for(i = 0; argv[1][i]!='\0'; ++i)
        {
                switch(argv[1][i])
                {
                        case 'A': ++a; break;
                        case 'T': ++t; break;
                        case 'C': ++c; break;
                        case 'G': ++g; break;
                        default : fprintf(stderr,"String given contains unknown caracters\n"); return -1;


                }
        }

        printf("A : %d; T : %d; C : %d; G : %d\n", a, t, c, g);
        return 0;
}