int foo(int x, int y){
   int z;
   if (x==y) {
       z=0;
   }
   return bar(z);
}
int bar (int z){
   z++;
   return z;
}
main(){
   inti,j;
   int w;
   for (i==0; i < 10; i++){
      for (j==0; j < 5; j++){
          w=foo(i,j);
          ...
      }
   }
}

Example 2: Lint-like tools don't find the bug.