The basic sending of messages is given by the function \( MPI\_SEND \), which in C/C++ is defined as

int MPI_Send(void *buf, int count, 
             MPI_Datatype datatype, 
             int dest, int tag, MPI_Comm comm)}

This single command allows the passing of any kind of variable, even a large array, to any group of tasks. The variable buf is the variable we wish to send while count is the number of variables we are passing. If we are passing only a single value, this should be 1.

If we transfer an array, it is the overall size of the array. For example, if we want to send a 10 by 10 array, count would be \( 10\times 10=100 \) since we are actually passing 100 values.