plotting data txt array

good day guys, i am making some work for college now, and well i am 
doing some kind of dft, discrete fourier transform basics, right now i 
am approximating sine waves by means of sampling, and some spicing. The 
problem is i do have the results in a txt file, yes that was the home 
work to work out some algorithm to have this txt data and view it on 
console, but i want to go a step furter, well i have the txt data why 
not plotting it, so far i tried mathgl, but well i could not do it, i 
did some google but not much found, so i come to you, there is some 
place where i can learn view, or copy the way of ploting data using gd 
and pure c code or cpp.

p.s. I tried koolplot also, and some other libraries.