How do you get all the weapons in GTA3

By GTAIII do you mean GTA III, Vice City or San Andreas? And for which platform, as the PS2, XBox, and PC versions all have different codes. Mobile versions don't have cheats.
All cheats can be entered at any time during gameplay. Be warned, though, as they will affect your game's save state.

GTAIII -

• PC:
• GUNSGUNSGUNS

• XBox:
• Black, black, L, Black, Left, Down, Right, Up, Left, Down. Right, Up

• PS2:
• R2, R2, L1, R2, Left, Down, Right, Up, Left, Down, Right, Up

GTA III : Vice City - PC:

• All Weapons #1
• THUGSTOOLS

• All Weapons #2
• PROFESSIONALTOOLS

• All Weapons #3
• NUTTERTOOLS

PS2:

• All Weapons #1
• R1, R2, L1, R2, Left, Down, Right, Up, Left, Down, Right, Up

• All Weapons #2

• R1, R2, L1, R2, Left, Down, Right, Up, Left, Down, Down, Left

• All Weapons #3

• R1, R2, L1, R2, Left, Down, Right, Up, Left, Down, Down, Down

XBox:

• All Weapons #1
• R, Black, L, Black, Left, Down, Right, Up, Left, Down, Right, Up

• Get Weapons #2
• R, Black, L, Black, Left, Down, Right, Up, Left, Down, Down, Down

• Get weapons #3
• R, Black, L, Black, Left, Down, Right, Up, Left, Down, Down, Left

GTA III : San Andreas -

PC:

• All Weapons #1
• LXGIWYL

• All Weapons #2
• PROFESSIONALSKIT

• All Weapons #3
• UZUMYMW

PS2:

• All Weapons #1
• R1, R2, L1, R2, Left , Down , Right , Up , Left , Down , Right , Up

• All Weapons # 2
• R1, R2, L1, R2, Left , Down , Right , Up , Left , Down, Down, Left

• All Weapons #3
• R1, R2, L1, R2, Left , Down , Right , Up , Left , Down, Down, Down

XBox:

• All Weapons #1
• R , Black , L , Black , Left , Down , Right , Up , Left , Down , Right , Up

• All Weapons #2
• R , Black , L , Black , Left , Down , Right , Up , Left , Down, Down, Left

• All Weapons #3
• R , Black , L , Black , Left , Down , Right , Up , Left , Down, Down, Down