Warning error on gcc compilation since maverick install

Question

Since I have installed Maverick on my mac, I have several issues to compile my C++ programs.
Following what I could read on some forum i installed xcode-select --install.
But now I have several Warning that I didn't have before. So I'm not sure my program is working correctly. Can someone help me.
Here is the Warning I got :
ML.c:743:3: warning: implicit declaration of function 'dgeev_' is invalid in C99 [-Wimplicit-function-declaration]
  dgeev_("N", "V", &N, A, &LDA, WR, WI, VL, &LDVL, VR, &LDVR, WORK, &LWORK, &INFO );
  ^
ML.c:791:3: warning: implicit declaration of function 'dgetrf_' is invalid in C99 [-Wimplicit-function-declaration]
  dgetrf_(&row, &column, VR_inv, &LDA2, IPIV2, &INFO2 );
  ^
ML.c:800:3: warning: implicit declaration of function 'dgetri_' is invalid in C99 [-Wimplicit-function-declaration]
  dgetri_(&N2, VR_inv, &LDA2, IPIV2, WORK2, &LWORK2, &INFO3);
  ^
ML.c:865:16: warning: implicit declaration of function 'dgemm_' is invalid in C99 [-Wimplicit-function-declaration]
  output_dgemm=dgemm_("N","N", &M, &N, &K, &ALPHA, MatrixA, &LDA_dgemm, MatrixB, &LDB_dgemm, &BETA, MatrixC, &LDC_dgemm);
               ^
ML.c:919:16: warning: implicit declaration of function 'dgemv_' is invalid in C99 [-Wimplicit-function-declaration]
  output_dgemm=dgemv_("N", &M, &N, &ALPHA, pii, &LDA_dgemv, X1, &INCX,&BETA, hi, &INCY );      
               ^
ML.c:978:1: warning: control may reach end of non-void function [-Wreturn-type]
Thanks a lot for your support.
BR,

Answer 1

You haven't declared those functions. Also, there is a path through your code where a function that should return a value, doesn't.