work/source: In function ‘int main(int, char**)’:
work/source:27:28: error: ‘fopen’ was not declared in this scope
work/source:29:22: error: ‘fscanf’ was not declared in this scope
work/source:46:64: error: ‘sort’ was not declared in this scope
work/source:68:37: error: ‘fprintf’ was not declared in this scope
work/source:69:14: error: ‘fclose’ was not declared in this scope
work/source:71:20: warning: ignoring return value of ‘int system(const char*)’, declared with attribute warn_unused_result [-Wunused-result]
