Voters in Africa's biggest economy and most populous country, Nigeria, head to the polls this morning to elect a new president and lawmakers, in what is set to be a close contest amid rising frustration over cash and fuel shortages, unprecedented insecurity and surging inflation. President Muhammadu Buhari, who will complete his constitutionally allowed two terms in May, is not on the ballot. Voters will also choose new senators and members for the House of Representatives. Governorship races follow on March 11. A total of 18 candidates are vying for the presidency. We spoke to Prof Chris Isike, a Nigeria expert from the University of Pretoria.