Here's the absolutely smallest array sorting function in C. It's written by M. Douglas McIlroy of Dartmouth College, NH USA. Both versions of the function below are his, not mine, and carry his terms rather than this site's snippet license. It only 67 bytes long (ignoring new-line characters), which is ridiculously impressive. In the function s shown below, a is the starting address of the array, and b is the address of the last element plus one.

s(int*a,int*b)
{for(int*c=b,t;c>a;)if(t=*c--,*c>t)c[1]=*c,*c=t,c=b;}

This can be made even smaller using recursion and by inferring the type specifiers of global object declarations, which is a GCC hack. In the following function, n is the number of elements in the array a.

s(a,n)int*a;
{n-->1?s(a,n),s(a+1,n),n=*a,*a=a[1],a[n>*a]=n:0;}

The sorting function s is now only 61 bytes long!