Using Variables Variables form a very important aspect of every programming language. Variables are memory locations in which we can store a value. We can use that value at different places and we can change it. Suppose we want to write a program that makes our robot drive in a series of squares of increasing size. This can be achieved by increasing the value of MOVE_TIME after each square. But how can we do this? MOVE_TIME is a constant and constants cannot be changed. We need a variable instead. Variables can easily be defined in NQC. You can have 32 of these, and you can give each of them a separate name.

Making Squares #define TURN_TIME 85 int move_time; // define a variable task main() { move_time = 20; // set the initial value repeat(50) { OnFwd(OUT_A+OUT_C); Wait(move_time); // forward motion increases OnRev(OUT_C); Wait(TURN_TIME); } Off(OUT_A+OUT_C); }

Assignment Variable = expression; x = 7; x = x + 3; tar = x*3 + tar; Expressions are evaluated from with the following precedence. * / top level + - second level Thus, x = 3+4*2 ==> 11 x = (3+4)*2 ==> 14 x = 2+4/2 ==> 4 x = (2+4)/2 ==> 3 For operators at the same level of precedence the order is left to right.

bar = 1+ Random(4); // ramdom number between 1 and 5 X = SENSOR_1 +2; //adds 2 to the value of sensor on port 1 Some other variants of the assignment statement (borrowed from C) bar += 7; // adds 7 to bar same as bar=bar+7 bar -= 2; // subtracts 2 from bar same as bar=bar-7 bar *= 4; // multiplies bar by 4 same as bar=4*bar

Spiraling Squares #define TURN_TIME 85 int move_time; // define a variable task main() { move_time = 20; // set the initial value repeat(50) { OnFwd(OUT_A+OUT_C); Wait(move_time); // forward motion increases OnRev(OUT_C); Wait(TURN_TIME); move_time += 5; // increase the variable } Off(OUT_A+OUT_C); }