Error(s):

source_file.m:3:15: error: expected identifier or ‘(’ before ‘^’ token
 typedef void (^CompletionBlock)();//typedef + returntype (^blockName)(argumentType);
               ^
source_file.m:7:38: error: unknown type name ‘CompletionBlock’
 - (void)performActionWithCompletion:(CompletionBlock)completionBlock; // completionBlock new data type
                                      ^
source_file.m:15:38: error: unknown type name ‘CompletionBlock’
 - (void)performActionWithCompletion:(CompletionBlock)completionBlock
                                      ^
source_file.m: In function ‘-[SampleClass performActionWithCompletion:]’:
source_file.m:19:5: error: called object ‘completionBlock’ is not a function or function pointer
     completionBlock(); //calling block
     ^
source_file.m:16:1: note: declared here
 {
 ^
source_file.m: In function ‘main’:
source_file.m:29:46: error: expected expression before ‘^’ token
     [sampleClass performActionWithCompletion:^{NSLog(@"Completion is called to intimate action is performed.");}];
                                              ^