You can use "textscan" function to read formatted data from text file or string.
The below code helps you in finding the number of times "for" keyword appears in the function named "myfunction.m" submitted by students:
file = fopen('myFunction.m','r');
st = textscan(file,'%s');
fclose(file);
str = st{:};
assert(numel(find(strcmp(str,'for'))) <= 1,'Use only one for loop')
This can be kept as a pre - test which will generate a warning if there are multiple "for" keywords in the answer. You may keep a template for the function so that the function name is not tampered with. Hope this helps.
