prog.c:14:21: warning: implicitly declaring library function 'printf' with type 'int (const char *, ...)'
if(input == NULL) { printf("there is no string\n"); return NULL;}
^
prog.c:14:21: note: include the header <stdio.h> or explicitly provide a declaration for 'printf'
prog.c:29:4: warning: implicitly declaring library function 'sprintf' with type 'int (char *, const char *, ...)'
sprintf(buffer+index4,"%c",input[index3]);
^
prog.c:29:4: note: include the header <stdio.h> or explicitly provide a declaration for 'sprintf'
2 warnings generated.
/usr/bin/../lib/gcc/i586-linux-gnu/4.9/../../../i386-linux-gnu/crt1.o: In function `_start':
/build/glibc-5CYv_T/glibc-2.19/csu/../sysdeps/i386/start.S:111: undefined reference to `main'
clang: error: linker command failed with exit code 1 (use -v to see invocation)