OpenMP (Open Multi-Processing) is an application programming interface (API) that supports multi-platform shared memory multiprocessing in C, C++ and Fortran.
#Running OpenMP hello world program
sirisha@sirisha-Inspiron-3558:~/Pictures/openmp$ gcc -fopenmp ex.c
sirisha@sirisha-Inspiron-3558:~/Pictures/openmp$ export OMP_NUM_THREADS=4
sirisha@sirisha-Inspiron-3558:~/Pictures/openmp$ ./a.out
#Output
hello world hello world hello world hello world