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POTwo questions of c++ which just change a little,however very different answers
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  1. POTwo questions of c++ which just change a little,however very different answers
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    copied!<p>Recently I do a exercise about algorithm with c++. Exercise in here:<a href="http://poj.org/problem?id=3083" rel="nofollow">poj</a></p> <p>I find two very confused questions. I write a class MAZE and there are three primary functions in MAZE,they are <code>int left_path();int right_path();int mini_path();</code> and a function to print the answers:</p> <pre><code>void display(){ cout&lt;&lt;left_path()&lt;&lt;" "&lt;&lt;right_path()&lt;&lt;" "; cout&lt;&lt;mini_path()&lt;&lt;endl; } </code></pre> <p>the program can work correctly.As we see the function display() can be easy; I write like this </p> <pre><code>void display(){ cout&lt;&lt;left_path()&lt;&lt;" "&lt;&lt;right_path()&lt;&lt;" "&lt;&lt;mini_path()&lt;&lt;endl; } </code></pre> <p>just one change ;however the program can't work,it like loop infinitely.</p> <p>following is the other question: the function mini_path's frame like this</p> <pre><code>int maze::mini_path(){ ini(); queue&lt;pair&lt;int,int&gt; &gt; q; q.push(make_pair(x,y)); while(!q.empty()){ pair&lt;int,int&gt; tmp=q.front(); q.pop(); int t=...; if(E){ return t; } if(E){ S } if(E){ S } if(E){ S } if(E){ S } } return -1; } </code></pre> <p>if there is "return -1" in the end ,the function works right,else the function return random big number.</p> <p><strong>The program is in only one file and i use the gun compiler.</strong></p> <p><strong>I don't show the total codes,because i think nobody wants to see them.I just want to ask what problems may lead above strange behaviors.</strong></p> <p>source code(simplified for question2):</p> <pre><code> typedef enum {LEFT=-1,RIGHT=1,UP,DOWN} direction; ifstream fin("file_test3.txt"); class maze{ public: maze(){input();} int mini_path(); void input(); void display(){ cout&lt;&lt;mini_path()&lt;&lt;endl; } private: bool is_not_dest(){ return !(x==d_x &amp;&amp; y==d_y); } void ini_dir() { if(e_x==0) dir=DOWN; else if(e_x==height-1) dir=UP; else if(e_y==0) dir=RIGHT; else dir=LEFT; } void ini(){ x=e_x; y=e_y; path_lenth=1; ini_dir(); } direction dir,d; int width,height,maze_map[40][40],path_lenth; int x,y,e_x,e_y,d_x,d_y; }; void maze::input() { fin&gt;&gt;width&gt;&gt;height; char sym; for(int i=0;i&lt;height;++i) for(int j=0;j&lt;width;++j){ fin&gt;&gt;sym; if(sym=='#') maze_map[i][j]=1; else if(sym=='.') maze_map[i][j]=0; else if(sym=='S'){ maze_map[i][j]=-1; e_x=i; e_y=j; } else { maze_map[i][j]=-2; d_x=i; d_y=j; } } } int maze::mini_path() { ini(); queue&lt;pair&lt;int,int&gt; &gt; q; if(dir==LEFT) {maze_map[x][--y]=2;} else if(dir==RIGHT) {maze_map[x][++y]=2;} else if(dir==UP) {maze_map[--x][y]=2;} else {maze_map[++x][y]=2;} q.push(make_pair(x,y)); while(!q.empty()){ pair&lt;int,int&gt; tmp=q.front(); q.pop(); x=tmp.first; y=tmp.second; int t=maze_map[x][y]+1; if((x==d_x &amp;&amp; (y-d_y==1 || y-d_y==-1)) ||(y==d_y &amp;&amp; (x-d_x==1||x-d_x==-1))){ return t; } if(maze_map[x-1][y]==0){ maze_map[x-1][y]=t; q.push(make_pair(x-1,y)); } if(maze_map[x+1][y]==0){ maze_map[x+1][y]=t; q.push(make_pair(x+1,y)); } if(maze_map[x][y-1]==0){ maze_map[x][y-1]=t; q.push(make_pair(x,y-1)); } if(maze_map[x][y+1]==0){ maze_map[x][y+1]=t; q.push(make_pair(x,y+1)); } } return -1; } main() { int n; fin&gt;&gt;n; while(n-- &gt;0){ class maze m; m.display(); } } </code></pre>
 

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