assembly - NASM add byte to register ebx -

is there simple way make nasm snippet work?

add ebx, byte [ebp-10+ecx]

i following error: error: mismatch in operand sizes. want add byte in memory address [ebp-10+ecx] least significant byte of ebx. of course ebx 4 or 8 byte register , causes error.

you can load byte 32 bit register using zero-extend move instruction, , use add ebx:

movzx eax,byte ptr [ebp-10+ecx] add ebx,eax 

or, if want perform 8-bit addition , don't care rest of bits of ebx, add byte lowest part of ebx. aware won't carry bit 7 bit 8 in ebx)

add bl,byte ptr [ebp-10+ecx] 

you can add signed byte 32 bit number using movsx instruction instead of movzx. movsx stands "move sign extend".