.NET Fiddle

CSharp · Console

/Program.cs

using System;
using System.Collections.Generic;

string [] mots = new []
{
   "bonjour", "coucou", "allo", "coucou", "yo", "bonjour", "coucou"
};
foreach(var (Mot, Nb) in CompterOccurrences(mots))
   Console.WriteLine($"Le mot {Mot} apparaît {Nb} fois");

static int TrouverIndice(List<(string Mot, int Nb)> mots, string mot)
{
   for(int i = 0; i != mots.Count; ++i)
      if(mots[i].Mot == mot)
         return i;
   return -1;
}
static (string Nom, int Nb)[] CompterOccurrences(string [] mots)
{
   List <(string Mot, int Nb)> lst = new ();
   foreach(string mot in mots)
   {
      int ndx = TrouverIndice(lst, mot);
      if(ndx == -1)
         lst.Add((mot, 1));
      else
         lst[ndx] = (mot, lst[ndx].Nb + 1);
   }
   return lst.ToArray();
}