Error(s):

source_file.cpp: In function ‘int main()’:
source_file.cpp:12:11: error: ‘o’ was not declared in this scope
    return o;  
           ^
source_file.cpp:11:20: warning: ignoring return value of ‘int system(const char*)’, declared with attribute warn_unused_result [-Wunused-result]
    system ("PAUSE");
                    ^