what is the wrong here

Answer 1

[David Hill]

h=.25;
t=0:h:1;
y=zeros(size(t));
y(1)=.1;%cannot start with y=0
f=@(t,y)(1+4*t)*sqrt(y);%I assume this is what you want
for i=1:length(t)-1
    y(i+1)=y(i)+h*f(t(i),y(i));
end
plot(t,y);
grid on;

Answer 2

[William]

David is probably right, but I made a different assumption about what equation you were trying to solve:

h = 0.25;
x = 0:h:1;
y = zeros(size(x));
y(1)=0;
n = numel(y);
t = 2;
for i=1:n-1
    f = (1+4*t)*sqrt(x(i));
    y(i+1)=y(i)+h*f;
end
plot(x,y);
grid on;