How to set instance variables from an NSMutableArray?

Is there a way to achieve what I am asking? After 2.5 hours of searching, I still have come up with nothing. Just finding solutions for animation frames.

You seem to want a variable whose value is another variable, so that you can iterate over a set of ivars. I can think of two ways to do something like what you're asking.

The first way is to use the address of each variable, i.e. a pointer to each variable. Since pointers themselves are scalar values, not objects, you'd need to use a C-style array:

CCSprite *ivars[] = {&dinosaur1_c, &dinosaur2_c, &dinosaur3_c, &dinosaur4_c};
for (int i = 0; i < 4; i++) {
    *(ivars[i]) = [dinoSprites objectAtIndex:i];
}

The second way is to use key value coding. Construct the name of each ivar as a string, and then use that as the key in a call to -setValue:forKey: like this:

NSString *name;
for (int i = 0; i < [dinoSprites count]; i++) {
    name = [NSString stringWithFormat:@"dinosaur%d_c", i];
    [self setValue:[dinoSprites objectAtIndex:i] forKey:name];
}

All that said, I'd strongly encourage you to not take either of the preceding two approaches to your problem. It's very likely that there are much better solutions to your problem that don't involve having a separate ivar for each dinosaur. You've already got the dinosaurs in an array, so there's no need to create a separate ivar for each. As a general rule, if you ever find yourself creating numbered variables like this, you should probably step back and rethink what you're doing -- numbering your variables is a strong signal that you should be using an array instead.

So, in your case, I don't see any reason that you couldn't use the array you already have everywhere in your code. Instead of dinosaur6_c, you can obviously use [dinoSprites objectAtIndex:6]. But you'll really clean up your code if you think of ways to treat all the dinosaurs with the same code, so that you're never hard-coding specific indicies into your array. For example, if you need to set each dinosaur to a different position, there are at least two good ways to go about it. One is to compute the position, if possible, based on the index. You can do this if you're laying out the dinosaurs in a regular way, like on a 3 x n grid:

for (int i = 0; i < [dinoSprites count]; i++) {
    int row = i / DINOS_PER_ROW;
    int column = i % DINOS_PER_ROW;
    CGPoint position = CGPointMake(row * rowHeight, column * columnWidth);
    [[dinoSprites objectAtIndex:i] setPosition:position];
}

If the position of each dinosaur isn't computable from its index in the array, then you're probably currently hard-coding the positions in your code. You can clean that up by at least moving the positions to an array, and perhaps by reading that array in from a data file. That will make your code much shorter, easier to understand, and easier to maintain:

NSArray *positions = [NSArray arrayWithContentsOfURL:someURL]; // read positions from a property list
NSAssert([positions count] >= [dinoSprites count], @"Not enough positions!");
for (int i = 0; i < [dinoSprites count]; i++) {
    CGPoint position = [[positions objectAtIndex:i] pointValue];
    [[dinoSprites objectAtIndex:i] setPosition: position;
}

Of course, I'm just using the position of the sprite here as an example. You can do exactly the same thing with any attribute that you'd want to apply to a dinosaur, and you can even do them all at once. Instead of a positions array that you load from a property list, you could load an array of dictionaries, where each dictionary contains a number of attributes (color, favorite food, speed, hunger level, etc.).