make a legend display a variable input

I'm trying to add a legend in a figure where the input of the legend is variable. I want a plot which displays 4-6 conditions with a legend that displays the corresponding conditions.

The code below is only to illustrate what i want to create. The first for-loop(for plotting) is of no importance.

 clc
close all
clearvars
tst = [ 12 21 14 18];
ntst = numel(tst);

for w=1:ntst
    hold on
    x=linspace(1,100);
    y=sin(x+x*tst(w));
    plot(x,y,'Color',[rand(1),rand(1),rand(1)])
end

b='';
for a=1:ntst
    b=[num2str(tst(a)),' test'];
end
legend(b,'Location', 'southeast')

The actual function has a matrix that contains data for 4-6 conditions and there is no need to plot it in a loop. The text that i want to display in the legend is formatted the same as 'tst' in the code above.

Answer 1

[Jos (10584)]

% an example
x = -10:10 ;
color = {'r','g','b','k'} ;
hold on ;
for k=1:4,
    y = (k-2) * x + k ;
    ph(k) = plot(x,y,'.-') ;
    set(ph(k),'color',color{k}) ;
    legendstr{k} = sprintf('%d * x + %d',[k-2 k]) ;
end
hold off
legend(ph,legendstr)

[Jacco vD]

well, it didn't work for me, but it made me show a mistake i made using {}, i tried it before but the code was different then so THX for reminding me :)