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    <p>The problem is that in each 'then' clause of the various <code>if</code> statements, you're creating a new local variable named <code>str</code>, assigning it to a new string, and then the variable goes out of scope. The compiler warning should tick you off to this: you're writing to a variable but never reading from it.</p> <p>Ordinarily, your code wouldn't compile, but you apparently have another variable named <code>str</code> in scope later on. Your new definitions of <code>str</code> are <em>shadowing</em> the old one: while the new name <code>str</code> is in scope, the name <code>str</code> refers to that variable, not the outer one, and the outer one is cannot be referred to.</p> <p>The solution is to move the declaration of <code>str</code> up to the top of the function. Furthermore, it's simpler just to use <code>[NSString stringWithFormat:@"blah"]</code> instead of <code>[[NSString alloc] initWithFormat:@"blah"]</code>, since the former gives you an autoreleased object. This saves you from having to manually <code>release</code> it later on. Note that assigning <code>lab.text=str</code> retains it, since the <code>text</code> property of the <code>UILabel</code> class has the <code>retain</code> modifier.</p> <pre><code>-(IBAction)buttonclick:(id)sender { NSString *title=[sender titleForState:UIControlStateNormal]; NSString *str; if([title isEqualToString:@"hello"]) { str=[NSString stringWithFormat:@"abc"]; } else if([title isEqualToString:@"nothing"]) { str=[NSString stringWithFormat:@"def"]; } else if([title isEqualToString:@"heaven"]) { str=[NSString stringWithFormat:@"ijk"]; } lab.text=str; } </code></pre> <p>Also note that with your original code, you had both a memory leak and memory corruption -- since you were allocating a string and then losing a reference to it (by the new local variable <code>str</code> going out of scope) without releasing it, and then you were calling <code>release</code> an extra time on whatever the outer <code>str</code> variable was. Moving the <code>str</code> declaration to the top of the function fixes both problems.</p> <p>I'm also assuming that your format strings are more complicated than just plain strings. If you're actually assigning constant strings such as <code>"abc"</code>, then of course it's much simpler to just do <code>str=@"abc"</code> instead of <code>str=[NSString stringWithFormat:@"abc"]</code>.</p>
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