I switched my compiling options in MSVC++ to compile in release mode instead of debug mode.

When it was compiling in debug mode, in compiled completely okay, but then when I just switched it to release mode, it suddenly gave me 40 linking errors.

They are below if you feel like looking at them...

but anyways, why did it just suddenly start giving me linking errors just by switching from debug mode to release mode???

Code:
Compiling...
main.cpp
Linking...
main.obj : error LNK2001: unresolved external symbol _gluPerspective@32
main.obj : error LNK2001: unresolved external symbol __imp__glLoadIdentity@0
main.obj : error LNK2001: unresolved external symbol __imp__glMatrixMode@4
main.obj : error LNK2001: unresolved external symbol __imp__glViewport@16
main.obj : error LNK2001: unresolved external symbol __imp__glClearColor@16
main.obj : error LNK2001: unresolved external symbol __imp__glShadeModel@4
main.obj : error LNK2001: unresolved external symbol __imp__glEnable@4
main.obj : error LNK2001: unresolved external symbol _SDL_PollEvent
main.obj : error LNK2001: unresolved external symbol __imp__glDisable@4
main.obj : error LNK2001: unresolved external symbol _SDL_EnableKeyRepeat
main.obj : error LNK2001: unresolved external symbol _SDL_Quit
main.obj : error LNK2001: unresolved external symbol _SDL_SetVideoMode
main.obj : error LNK2001: unresolved external symbol _SDL_GL_SetAttribute
main.obj : error LNK2001: unresolved external symbol _SDL_Init
main.obj : error LNK2001: unresolved external symbol _SDL_GL_SwapBuffers
main.obj : error LNK2001: unresolved external symbol __imp__glTranslatef@12
main.obj : error LNK2001: unresolved external symbol __imp__glRotatef@16
main.obj : error LNK2001: unresolved external symbol __imp__glClear@4
main.obj : error LNK2001: unresolved external symbol _auxDIBImageLoadA@4
main.obj : error LNK2001: unresolved external symbol __imp__glTexImage2D@36
main.obj : error LNK2001: unresolved external symbol __imp__glBindTexture@8
main.obj : error LNK2001: unresolved external symbol __imp__glGenTextures@8
main.obj : error LNK2001: unresolved external symbol __imp__glTexParameteri@12
main.obj : error LNK2001: unresolved external symbol __imp__glEnd@0
main.obj : error LNK2001: unresolved external symbol __imp__glVertex3f@12
main.obj : error LNK2001: unresolved external symbol __imp__glColor3f@12
main.obj : error LNK2001: unresolved external symbol __imp__glBegin@4
main.obj : error LNK2001: unresolved external symbol __imp__glTexCoord2f@8
main.obj : error LNK2001: unresolved external symbol __imp__glEndList@0
main.obj : error LNK2001: unresolved external symbol __imp__glTranslated@24
main.obj : error LNK2001: unresolved external symbol __imp__glNewList@8
main.obj : error LNK2001: unresolved external symbol __imp__glVertex2i@8
main.obj : error LNK2001: unresolved external symbol __imp__glGenLists@4
main.obj : error LNK2001: unresolved external symbol __imp__glDeleteLists@8
main.obj : error LNK2001: unresolved external symbol __imp__glPopMatrix@0
main.obj : error LNK2001: unresolved external symbol __imp__glCallLists@12
main.obj : error LNK2001: unresolved external symbol __imp__glListBase@4
main.obj : error LNK2001: unresolved external symbol __imp__glOrtho@48
main.obj : error LNK2001: unresolved external symbol __imp__glPushMatrix@0
LIBC.lib(wincrt0.obj) : error LNK2001: unresolved external symbol _WinMain@16
Release/RTS Practice.exe : fatal error LNK1120: 40 unresolved externals
Error executing link.exe.

RTS Practice.exe - 41 error(s), 0 warning(s)