Down sampling in MATLAB without built in function in MATLAB

Code:-

clc

clear all

close all

warning off

n=input('Enter the time sample range:');

x=input('Enter the amplitudes:');

a=input('Enter the scaling factor:');

e=[];

temp=1;

for i=1:length(n)

    e=[e ;n(temp) x(temp)];

    temp=temp+1;

end

z=[];

for i=1:length(e)

    if(rem(e(i,1),a)==0)

        z=[z;e(i,:)];

    end

end

index=z(:,1);

amplitude=z(:,2);

rs=find(index>=0);

temp=0;

for i=1:length(rs)

    index(rs(i))=temp;

    temp=temp+1;

end

gs=find(index==0);

temp=-1;

for i=(gs-1):-1:1

    index(i)=temp;

    temp=temp-1;

end

stem(index,amplitude);