... To use system calls and library functions in a C program we simply call the appropriate C function (Appendix ). We have already met some system calls when dealing with low level I O - open(), creat(), read(), write() and close() are examples. ... All math functions such as sin(), cos(), sqrt() and random number generators - random(), seed(), lrand48(), drand48() etc. are standard math library functions. NOTE: most standard library functions will use system calls within them. ...