I want to execute another program within C code.
For example, I want to execute a command
./foo 1 2 3
1 2 3
int status = system("./foo 1 2 3");
system() will wait for foo to complete execution, then return a status variable which you can use to check e.g. exitcode.
man 2 wait on your linux system will list the various macros you can use to examine the status, the most interesting ones would be
Alternatively, if you need to read foo's output to stdout, use