About Frameshift Mutation
Genes (here defined as protein coding sequences) are not perfectly aligned the ones after the others in the genome. In fact, in humans (like in most eukaryotes), only a small fraction (of the order of the percent) of the genome directly code for proteins.

Each gene translation unit starts with specific markers. Not even talking about what will be or won't be transcribed, a translation unit starts with the start codon (AUG). Hence, a frameshift mutation will only affect the gene in which (or even, only the exon) in which the mutation happened.

For writing a software that finds coding sequences (and translate them), you will need to learn much more about genetics. You might want to have a look at an intro course on molecular genetics / central dogma / translation, transcription such as a number of the biology classes on Khan Academy for examples.