warning: assignment makes pointer from integer without a cast错误

if((in=fopen("read.in","r"))==NULL)

 

没注意运算符的优先级，导致了warning: assignment makes pointer from integer without a cast错误，好久才找出来

原语句是这样的：

if(in=fopen("read.in","r")==NULL)

分析：由于==的优先级高于=，所以会先计算fopen("read.in","r")==NULL这个表达式，这个表达式的计算结果会是TRUE or FAILUER，也就是int型，而in是char*，所以将int型赋值给char*，就会报warning: assignment makes pointer from integer without a cast这样的错误。

修改：

if if(（in=fopen("read.in","r")）==NULL)

这样就ok了。