Week 2 - Friday

 What did we talk about last time?  Base systems  C literals  Representations in memory

It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so. Mark Twain It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so. Mark Twain

FunctionResultFunctionResult cos(double theta) Cosine of theta exp(double x) ex ex sin(double theta) Sine of theta log(double x) Natural logarithm of x tan(double theta) Tangent of theta log10(double x) Common logarithm of x acos(double x) Arc cosine of x pow(double base, double exponent) Raise base to power exponent asin(double x) Arc sine of x sqrt(double x) Square root of x atan(double x) Arc tangent of x ceil(double x) Round up value of x atan2(double y, double x) Arc tangent of y/x floor(double x) Round down value of x fabs(double x) Absolute value of x fmod(double value, double divisor) Remainder of dividing value by divisor

 You must #include to use math functions #include int main() { double a = 3.0; double b = 4.0; double c = sqrt(a*a + b*b); printf("Hypotenuse: %f\n", c); return 0; } #include int main() { double a = 3.0; double b = 4.0; double c = sqrt(a*a + b*b); printf("Hypotenuse: %f\n", c); return 0; }

 Just using #include gives the headers for math functions, not the actual code  You must link the math library with flag –lm  Now, how are you supposed to know that? > gcc -lm hypotenuse.c -o hypotenuse > man 3 sqrt

 Man (manual) pages give you more information about commands and functions, in 8 areas: 1. General commands 2. System calls 3. Library functions (C library, especially) 4. Special files and devices 5. File formats 6. Miscellaneous stuff 7. System administration  Try by typing man topic for something you're interested in  If it lists topics in different sections, specify the section  For more information: > man 3 sqrt > man man

 We haven't talked about any input in C yet  To read the next character from input, you can use the getchar() function  It will return the value of the next character (as an int ) or -1 if the end of the file is reached  Store the value as an int first to check to see if the end of the file has been reached  If not, you can then store it as a char int value = getchar(); if( value == -1 ) printf("End of file!"); int value = getchar(); if( value == -1 ) printf("End of file!");

 putchar() is the output equivalent of getchar()  It outputs a single character at a time  You could use printf() with the %c formatter instead, but putchar() can be more convenient for single characters char letter = 's'; putchar('q'); putchar(letter); char letter = 's'; putchar('q'); putchar(letter);

 There are preprocessor directives which are technically not part of the C language  These are processed before the real C compiler becomes involved  The most important of these are  #include  #define  Conditional compilation directives

 You have already used #include before  #include  It can be used to include any other file  Use angle brackets ( ) for standard libraries  Use quotes ( " " ) for anything else  It literally pastes the file into the document where the #include directive is  Never #include.c files (executable code), only.h files (definitions and prototypes)  It is possible to have a circular include problem

 The primary way to specify constants in C is with a #define  When you #define something, the preprocessor does a find and replace  Don't use a semicolon!  #define directives are usually put close to the top of a file, for easy visibility #define SIZE 100 int main() { int array[SIZE]; int i = 0; for( i = 0; i < SIZE; i++ ) array[i] = i*i; return 0; } #define SIZE 100 int main() { int array[SIZE]; int i = 0; for( i = 0; i < SIZE; i++ ) array[i] = i*i; return 0; }

 You can also make macros with #define that take arguments  You need to be careful with parentheses  Constants and macros are usually written in ALL CAPS to avoid confusion #include #define TO_DEGREES(x) ((x) * ) #define ADD(a,b) ((a) + (b)) int main() { double theta = TO_DEGREES(2*M_PI); int value = ADD(5 * 2, 7); return 0; } #include #define TO_DEGREES(x) ((x) * ) #define ADD(a,b) ((a) + (b)) int main() { double theta = TO_DEGREES(2*M_PI); int value = ADD(5 * 2, 7); return 0; }

 You can use directives #if, #ifdef, #ifndef, #else, #elif and #endif  These are mostly used to avoid infinite include problems  Sometimes they will change what gets compiled based on compiler version, system libraries, or other stuff #ifndef SOMETHING_H #define SOMETHING_H int something(int a, int b); #endif #ifndef SOMETHING_H #define SOMETHING_H int something(int a, int b); #endif

 System limits  const  Bitwise operators  Operator precedence

 Keep reading K&R chapter 2