Note that you should not use numbered variables, as this invariably leads beginners to dynamic variable naming, which is a very poor programming practice. Instead you should note that these numbers are essentially indices, in which case actually make them real indices. Read this to know why numbered variables are a bad idea:
And this to know why dynamically naming variable is an even worse idea:
Also using if's and loops is slow and inefficient: MATLAB works best when you learn how to write vectorized code, and to not use loops to solve every little task. Try this:
prompt={'1st Note','2nd Note','3rd Note','4th Note','5th Note','6th Note','7th Note'};
name='Enter Note Values (C-B)..';
defaultans={'C','D','E','F','G','A','B'};
answer=inputdlg(prompt,name,[1,50],defaultans);
% These three lines replace all of your loop and elseif statements:
V = 'CDEFGAB';
idx = cellfun(@(c)find(V==c),answer);
frq = [261.626,293.665,329.628,349.228,391.995,440.000,493.883];
out = frq(idx)
