Converting binary to decimal depends on whether the binary pattern is to interpreted as representing only positive values or to use some convention to also represent negative values. C uses unsigned integer types for the first case.
Bits are numbered 0 to 7 from the LSB (least significant bit) to the
MSB (most significant bit)
binary representation: 00011101
bit position: 76543210
The value of a bit at position k is multiplied by 2k.
A 1 bit in position 4 is worth 24 or 16.
A 1 bit in position 3 is worth 23 or 8.
So for the 8 bits of a 1 byte integer, the multiplers for each bit
position are:
_ _ _ _ _ _ _ _
128 64 32 16 8 4 2 1
For the value 00011101,
0 0 0 1 1 1 0 1
_ _ _ _ _ _ _ _
128 64 32 16 8 4 2 1
the corresponding decimal value is 16*1 + 8*1 + 4*1 + 1*1 = 29