TheDetermination/MyFirstAnalysisInDNA

Here, my first program for DNA analysis, you can see the dna bases (A,T,G,C) as well as you can count how many bases in your DNA file; for example,"AAGGTTCCAGTC" here you can count them,A=3,T=3,G=3 and C=3. What if i have 3 billions of bases ? how can i count them ?