der Präsident
president
The head of state in a republic.
Der französische Präsident besucht nächste Woche Berlin.
The French president is visiting Berlin next week.

president
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president
The head of state in a republic.
Der französische Präsident besucht nächste Woche Berlin.
The French president is visiting Berlin next week.

'Der Präsident' (president) is a noun of the N-declension. This means it takes the ending '-en' in the genitive, dative, and accusative singular. Learners often make mistakes with this.
Ich habe den Präsidenten gestern im Fernsehen gesehen.
I saw the president on television yesterday.
You can tell from context whether the head of state or the head of an organization is meant. In connection with country names, it means the head of state; with clubs or companies, it means the leader.
Der amerikanische Präsident hält eine Rede.
The American president is giving a speech.
In the context of organizations, the construction 'jemanden zum Präsidenten wählen' (to elect someone president) or 'zum Präsidenten ernannt werden' (to be appointed president) is often used.
Sie wurde zur neuen Präsidentin des Unternehmensverbands gewählt.
She was elected the new president of the business association.
king
'der König' and 'der Präsident' can both be the head of state of a country. The important difference lies in the form of government. A 'König' belongs to a monarchy and usually gets his role through his family. A 'Präsident' belongs to a republic and is normally elected or chosen through a political process. Learners may confuse the words because both can stand at the head of a state. So pay attention to the country and its form of government: monarchy with a king, republic with a president.

Der Präsident wurde für vier Jahre gewählt.
The president was elected for four years.
Der König hielt vor dem Parlament eine kurze Rede.
The king gave a short speech before parliament.