Insert a string in middle of another string

.model small .stack 100h .data msg1 db 'Enter 1st string $' msg2 db 'Enter 2nd string $' msg4 db 'Result string is-> $' s1 db 50 dup('$') s2 db 50 dup('$') s3 db 50 dup('$') len1 dw ? len2 dw ? pos dw 0 .code main proc mov ax,@data mov ds,ax mov es,ax ;display 'enter 1st string' lea dx,msg1 call display ;read the 1st string lea di,s1 call readstr endinpt:mov len1,cx ;jump to nextline call newline ;display 'enter 2nd string' lea dx,msg2 call display ;read the 2nd string lea di,s2 call readstr endinp1:mov len2,cx ;find the position xor dx,dx mov ax,len1 mov bx,02h div bx mov pos,ax ;insert a string into another string endpos: xor cx,cx lea si,s1 lea di,s3 cld mov cx,pos rep movsb mov dx,si lea si,s2 mov cx,len2 rep movsb mov cx,len1 sub cx,pos mov si,dx rep movsb ;jump to nextline call newline ;display 'Result string is-> ' lea dx,msg4 call display ;print result string lea dx,s3 call display mov ah,4ch int 21h main endp display proc mov ah,09h int 21h ret display endp newline proc mov dl,0ah mov ah,02h int 21h ret newline endp readstr proc xor cx,cx cld loop1: mov ah,01 int 21h cmp al,0dh je endread stosb inc cx jmp loop1 endread:ret readstr endp end