title: Beginner's query about C program Function Call stack, sequence point(sequencing)
body: <p>The code below displays different results when compiled and run on Code::Blocks.</p>
  
  <pre><code>void sum(int a,int b){
      printf("a=%d b=%d\n",a,b);
  }
  int main(){
      int i=1;
      sum(i=5,++i);
      printf("i=%d\n\n",i);
      /***********************/
      i=2;
      sum(i=5,i++);
      printf("i=%d\n\n",i);
      /**********************/
      i=3;
      sum(i=5,i);
      printf("i=%d\n\n",i);
      return 0;
  }
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>a=5 b=5
  i=5
  
  a=5 b=2
  i=5
  
  a=5 b=5
  i=5
  </code></pre>
  
  <p>I think the answer to this question is related to sequence point and the sequence point is related to ++ operator here. GCC must be following an order to pass the value to stack in a fixed order but because of ++ the answers are different. I think for a beginner to write a function call like this is not very common, but the lesson about operators are general so one can try.</p>
  
  <p>My questions are,what should be the exact answer of it and questions like it? During which phase of compilation these things are decided(made it clear or unclear)? Which particular algorithm(s) (either for optimization or in general) is involved? Can same compiler provide different result for such expression or statements? And the last on is, how a beginner will understand and figure out these problems? It is sometimes very surprising.</p>