try this:
B = readtable('hw3.txt','ReadVariableName',false,'delimiter',':');
data2=B(:,2);
data3=table2array(B(:,2));
data4=str2double(split(data3,','));
a = 0;
b = 0;
c = 0;
d = 0;
e = 0;
f = 0;
g = 0;
h = 0;
j = 0;
k = 0;
for i = 1:45
if data4(i) >=0 && data4(i) <= 9
a = a + 1;
elseif data4(i) >= 10 && data4(i) <= 19
b = b + 1;
elseif data4(i) >= 20 && data4(i) <= 29
c = c + 1;
elseif data4(i) >= 30 && data4(i) <= 39
d = d + 1;
elseif data4(i) >= 40 && data4(i) <= 49
e = e + 1;
elseif data4(i) >= 50 && data4(i) <= 59
f = f + 1;
elseif data4(i) >= 60 && data4(i) <= 69
g = g + 1;
elseif data4(i) >= 70 && data4(i) <= 79
h = h + 1;
elseif data4(i) >= 80 && data4(i) <= 89
j = j + 1;
elseif data4(i) >= 90 && data4(i) <= 100
k = k + 1;
end
end
fprintf('0~9: %d\n', a);
fprintf('10~19: %d\n', b);
fprintf('20~29: %d\n', c);
fprintf('30~39: %d\n', d);
fprintf('40~49: %d\n', e);
fprintf('50~59: %d\n', f);
fprintf('60~69: %d\n', g);
fprintf('70~79: %d\n', h);
fprintf('80~89: %d\n', j);
fprintf('90~100: %d\n', k);
x = 0 : 10 : 100 ;
y = 7;
output=[a b c d e f g h j k]'
% h = histogram(output,'BinWidth',0.3)
bar(output,'BarWidth',0.05)
xlabel('Group Interval');
ylabel('No. of students');
title('Histogram of Grades');
