Output arguments in functions

In my code I have a some functions with an output argument c which seems to have caused some trouble as the errors are:

Error in image_processing_project>checkhorizontal (line 74)
for n = 0:steps

Output argument "c" (and maybe others) not assigned during call to
"C:\Users\bostock_h\Documents\MATLAB\image_processing_project.m>image_processing_project/checkhorizontal".

Error in image_processing_project/checkright (line 64)
c = checkhorizontal(i1,j,x1);

Error in image_processing_project (line 22)
    c = checkright (i1,j);

and here is the code:

function image_processing_project

M = imread('C:\Users\bostock_h\Documents\Images\130510_162.jpg');
M = int16(M);

x = 975;  %dimensions of the image
y = 1010;
sum=0;
global steps %the number of steps taken for the average
steps = 12;
global lowlimit %minimum value to pass
lowlimit = 40;
global highlimit %maximum value to pass
highlimit = 200;
global movel %amount of pixels moved to the left after check
movel = 10;
prog = 0; 
pixelnum = (x - movel - 1)*y; %Total number of pixels in the image
%Main loop begin
for j = 1:y
    for i1 = movel + 1:x
    c = checkright (i1,j); 

      if c ~= 0
          b = 1;
      else
          b = -1;
      end

      if c == 0
          c = checkleft (i1,j);
      end
      if c == -1 
          if b == 1
          M(j,i1-movel) = 1;
          end 
      end
      if c == 1
          if b == 1
          M(j,i1-movel) = 250;
          end 
      end 
      if c == 1
          if b == -1
          M(j,i1+movel) = 250;
          end 
      end
      if c == -1
          if b == -1
          M(j,i1+movel) = 1;
          end    
      end
      prog = prog + 1;
      percent = (prog / pixelnum) * 100
      end
  end

imagesc(M)
colormap(gray)

function c = checkright(i1,j)
x1 = 1;

c = checkhorizontal(i1,j,x1);
end

function c = checkleft(i1,j)
x1 = -1;

c = checkhorizontal(i1,j,x1);
end

function c = checkhorizontal(i1,j,x1)
for n = 0:steps
        sum = M(j, i1 + n*x1) + sum;
end 
avg = sum / steps;
if avg < lowlimit
    c = -1*x1;
end

if avg > highlimit
    c = 1*x1;
end
end
end

Answer 1

[Tom]

In the CHECKHORIZONTAL function:

if avg < lowlimit
    c = -1*x1;
end
if avg > highlimit
    c = 1*x1;
end

means that if avg is neither below the low limit nor above the high limt, it won't be created in the function. Try setting adding an else statement which specifies a value of c and see if that helps.

[Harry]

Thanks for the reply. I've changed that segment of code to:

   if avg < lowlimit
      c = -1*x1;
  else c = 0;
  end

if avg > highlimit
    c = 1*x1;
    else c = 0;
end

But that doesn't seem to have helped the errors regarding the c but has replaced the first error with a different one:

Subscript indices must either be real positive integers or logicals.

Error in image_processing_project/checkhorizontal (line 75)
        sum = M(j, i1 + n*x1) + sum;

Error in image_processing_project/checkleft (line 70)
c = checkhorizontal(i1,j,x1);

Error in image_processing_project (line 31)
        c = checkleft (i1,j);