Convert octal value into hex !?

The easiest way is to use binary as an intermediary step

oct 172 = bin 001 111 010 = hex 7A

It helps to group the bits to match the format. so 001 111 010 for oct is easier to conver written as (000)0 0111 1010.

suppose you have a binary number, you need to group them by 3 to get octal and the resulting digits are 0-7 to convert to hex, it's 4 bits so you have digits of 0-9 and A-F for example, F in hex is 1111 which is 17 in octal

the easiest way to go from octal to hex is to expand into binary. Every digit in octal is 3 bits in binary. So 0172 in binary is 001 111 010. Then, switch it from groups of 3 to groups of 4.

0 0111 1010. 0b0111 = 7 = 0x7, 0b1010 = 10 = 0xA, so your final result is 0x7A.

** my notation, if you've never seen it before: 0 = octal, 0b = binary, 0x = hex, nothing = decimal.