fprintf curiosity about incorrect value returned when string is assigned as a number.

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Jaimie Ritchie 2022-10-26

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评论： Jaimie Ritchie 2022-10-26

Hello,

I am learning about fprintf and I was playing around. I ended up with this string below. I realize now that in the second sentence it should be %s because it's printing a string.

But! Here's my question. I don't get returned an error message. Instead, I get that 10 + 34 is 52.

WHY? I want to know.

N = 10; S = 34;

fprintf('What is %g plus %g? It''s %g! \n', N , S, num2str(N + S))

When I use fprintf('What is %g plus %g? It''s %s! \n', N , S, num2str(N + S)) I get 44 as expected.

Can anyone tell me why 52 is the number returned when the string is commanded as a number?

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Answer 1

Walter Roberson 2022-10-26

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the sum is 44 and num2str(44) is '44' which is a character vector.

Every character is encoded as a 16 bit number, so the character vector '44' is encoded as pair of 16 bit numbers. The encoding for the digits 0 to 9 is integer 48 plus the digit value, so digit 4, '4' is encoded as 48+4 = 52. So you are passing in a vector of two values each of which happens to be 52 numerically, and the %g format would display the 52

If you looked closely you probably got an extra line

What is 52 plus

where it went to display the second '4'