Because that's what you asked for.
See here:
ASCII table[
^]
The "%c" specifier says "treat the input value as a character and print that". Look at the table, and find "100" under the "Dec" column - it's a lower case "d". Now look for "125" in the same column and it's "}".
So you asked it to print your value as a character, and that is exactly what it did.