how to use thumb mode ?

 AREA ToThumb, CODE, READONLY    ; Name this block of code
        ENTRY                           ; Mark first instruction to execute
        ARM                             ; Subsequent instructions are ARM 
start
        ADR     r0, into_thumb + 1      ; Processor starts in ARM state 
        BX      r0                      ; Inline switch to Thumb state
        THUMB                           ; Subsequent instructions are Thumb
into_thumb
        MOVS    r0, #10                 ; New-style Thumb instructions

...         // Thumb code
#pragma arm // ARM code. Switch code generation to the ARM instruction set so
            // that the inline assembler is available for Thumb in ARMv6 and lower.

int add(int i, int j)
{
    int res;
    __asm
    {
        ADD   res, i, j   // add here
    }
    return res;
}
#pragma thumb   // Thumb code. Switch back to the Thumb instruction set.
                // The inline assembler is no longer available for Thumb in ARMv6 and
                // lower.