string graphic = "abcdefghijklmnopqrstuvwxyz";
//Вариант 1
foreach (var g in graphic)
foreach (var t in graphic)
project.Variables["variables"].Value+= g + "" + t;
//Вариант 2
foreach (var g in graphic)
for (int i = 1; i < graphic.Length; i++)
project.Variables["variables"].Value+= g + "" + graphic[i];