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Numeric types of C. Integers Signed and unsigned In a few different sizes 209 Floating point In different size 209.602. Integer types by size. char Holds single characters short Holds small numbers int The usual integer long When 2,000,000,000 isn’t enough.
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Numeric types of C • Integers • Signed and unsigned • In a few different sizes • 209 • Floating point • In different size • 209.602
Integer types by size • char • Holds single characters • short • Holds small numbers • int • The usual integer • long • When 2,000,000,000 isn’t enough
What you can say about size? • short is at least as big as char • int is at least as big as short • long is a least as bit as int • I.E., not much
C Portability Problem • It’s hard to write portable programs • When you don’t know what an int will hold • More likely to be a problem with small chips • Such as embedded processors • sizeof(int) will give the size in bytes • But this is hard too use without macros
C99 as problem and solution • C99 adds an additional integer type • long long • At least as bit as long • Provides bit-length specific integers • int32_t i ; • Declares a 32-bit integer • If <inttype.h> is included
Unsigned • Useful when you know number is positive • As in counts • Gives you twice as many positive value • For 8 bit numbers which is it? • 00000001 > 11111111 • 00000001 < 11111111
Floating point types by size • float • Usually IEEE 754 32-bit single precision • double • Usually IEEE 754 64-bit double precision • long double • Often same as double • Could be IEEE 754-2008 128-bit “quad” precision • Could be Intel 80-bit “extended” precision
Integer literals • Decimal • 209 • Octal • 0321 • Hexadecimal • 0xD1 • Suffixes • U for unsigned • L for long
Floating point literals • With a dot but no exponent • 10.5, 1., .2 • With an exponent and possibly a dot • 2e20, .2e20, 2.e20, 2.2e20, 7e-15 • With possible suffixes • F for float • L for long
Default argument promotionEvil in C • If a char or short is an argument to printf • It is promoted to an int • If a float is an argument to printf • It is promoted to a double • printf cannot tell signed from unsigned The above statements aren’t quite true, but they are good enough for now. In a later chapter, you’ll learn about prototypes and all of this may become a little clearer.
Therefore … • printf “thinks” the following are identical • printf(” %c\n”, ’A’) ; • printf(” %c\n”, 65) ; • As are the following • printf(” %25.20f\n”, 3.1416f) ; • printf(” %25.20f\n”, 3.1416) ; • You may need to “tell” printf more or less than you think necessary
However • Assume • int and long int are different • double and long double are different • Because • They often take up more space on the stack • Unless they are the same length • Which often is the case • Isn’t this confusing
Length modifiers for integers • Can proceed the integer conversion specifier • Except for %c • Only useful one is l, as in printf(“Big number is %ld\n”, 20000000000000L) ; • There is also largely unneeded h and hh • Prints the short and char part of an int
Length modifiers for floating point • Use L for long double as in printf(“Big number is %Lf\n”, 2e2009L) ;
Input with scanf • To read numbers use scanf scanf(”%d”, &courseNumber) ; scanf(”%f”, &temperature) ; • Notice the & • It will be explained later in the course • It means “address of”
Conversion specifiers for scanf %X is the same as %x %F, %e, %E, %g, %G are the same as %f
Matching • scanf(”%d,%d”, &i, &j) ; • A comma must be between the numbers • scanf(”%d%%%d”, &i, &j) ; • A percent sign must be between the numbers