objective c - NSMutableArray array isn't created -

on line marked comment "right here" (the last if statement) compiler tells me "index 0 beyond bounds empty array" interpret - array wasn't created.

the idea - in last loop i'm going sum areas of existing triangles calc areas.

nsmutablearray *xcoordinate = [nsmutablearray array]; nsmutablearray *ycoordinate = [nsmutablearray array];  // code in here...  int t;  int g = [xcoordinate count];  if (g<3) {     printf("please enter @ least 3 value pairs form polygon\n");     return 0; }  nsmutablearray *arrayofcorners = [nsmutablearray array]; nsmutablearray *arrayoftriangls = [nsmutablearray array];   (t=0; t < g; t++) {      float x = [[xcoordinate objectatindex:t] floatvalue];     float y = [[ycoordinate objectatindex:t] floatvalue];      rectanglecorner *corner = [[rectanglecorner alloc] initwithx:x  andy:y];      // 3. add corner array.     [arrayofcorners addobject:corner];      if (t>=2) {          // 4. forming triangle.         triangle *triangle = [[triangle alloc] init];          // 5. calc sides length. calculate lengths , assignes values side1, side2, side3 properties of triangle.         [triangle sidelengthwithvert:arrayofcorners[t] vert2:arrayofcorners[t+1] vert3:arrayofcorners[t+2]];          // 6. calc triangle area.         [triangle calcarea];          // 7. adding triangle's area our array         [arrayoftriangls addobject:triangle];      }      // 8. adding areas of triangles (if have array of them)      int = 0;     nsinteger nsi = (nsinteger) i;      // right here.     triangle *testingtriangle = [arrayoftriangls objectatindex:nsi];     if (testingtriangle)     {          int y = [arrayoftriangls count];         int r;          (r=0; r<=y; r++) {              float p;              int q = r;             nsinteger ndi = (nsinteger) q;             triangle *triangle = [arrayoftriangls objectatindex:ndi];              p +=triangle.area;              printf("polygon's area %f", p);         }      }  } 

lets walk through code:

if (g<3) {     printf("please enter @ least 3 value pairs form polygon\n");     return 0; }  nsmutablearray *arrayofcorners = [nsmutablearray array]; nsmutablearray *arrayoftriangls = [nsmutablearray array]; (t=0; t < g; t++) { 

you create array of triangles before loop, go loop @ least g = 3.

now lets start t = 0, , go through loop:

    float x = [[xcoordinate objectatindex:t] floatvalue];     float y = [[ycoordinate objectatindex:t] floatvalue];      rectanglecorner *corner = [[rectanglecorner alloc] initwithx:x  andy:y];      // 3. add corner array.     [arrayofcorners addobject:corner];      if (t>=2) {          // 4. forming triangle.         triangle *triangle = [[triangle alloc] init];          // 5. calc sides length. calculate lengths , assignes values side1, side2, side3 properties of triangle.         [triangle sidelengthwithvert:arrayofcorners[t] vert2:arrayofcorners[t+1] vert3:arrayofcorners[t+2]];          // 6. calc triangle area.         [triangle calcarea];          // 7. adding triangle's area our array         [arrayoftriangls addobject:triangle];      } 

the if not true @ point, didn't add triangle yet array. triangle array contains 0 objects. lets move on:

    int = 0;     nsinteger nsi = (nsinteger) i;      // right here.     triangle *testingtriangle = [arrayoftriangls objectatindex:nsi]; 

now try object @ index 0, array contains 0 objects. suppose t >= 2 code works, t = 0, 1 code crashes.