order of parsing expressions

fxlj007 · Thu Oct 11, 2012 1:11 pm

Hi guys, I come across a really confusing problem. I have a function as below:


	Code: void mSetInstantMotion(float vx, float vy, float r){ int a = (int)(r + vx); int b = (int)(r-1vx-2vy); int c = (int)(r-1vx+2vy); motor[motorA] = a; motor[motorB] = b; motor[motorC] = c; while(true){EndTimeSlice();} }

Very simple. But from a snapshot of the local variables, i see:


	Quote: vx 50 vy 50 r 0 a 50 b 50 c -150

It doesn't match what I'm expect. It should be b = 0 - 50 -2*50 = -150 right? Also wrong for c = 0 - 50 + 2*50 = 50

It becomes correct if i parenthesize each product term, as below


	Code: void mSetInstantMotion(float vx, float vy, float r){ int a = (int)(r + vx); int b = (int)(r-(1vx)-(2vy)); int c = (int)(r-(1vx)+(2vy)); motor[motorA] = a; motor[motorB] = b; motor[motorC] = c; while(true){EndTimeSlice();} }

But this should not be necessary. It seems the compiler evaluates an expression from right to left, which seems awkward. Do you have any ideas about this?

order of parsing expressions

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