1. C Programming Functions Macros

2. Functions vs. Methods Java classes include methods which can be called from any code with appropriate access (recall public methods)Java classes include methods which can be called from any code with appropriate access (recall public methods) C functions are like Java methods, but they don’t belong to any class. Functions are defined in a file and may be either global to your program or local to (“private” in) the file in which they are defined*.C functions are like Java methods, but they don’t belong to any class. Functions are defined in a file and may be either global to your program or local to (“private” in) the file in which they are defined*. Like Java methods, C functionsLike Java methods, C functions –Have a name –Have a return type –May have parameters Unlike Java methods, a function in C is uniquely identified by its name. Therefore, there is no concept of method overloading in C as there is in Java. There can be only one main( ) function in a C application.Unlike Java methods, a function in C is uniquely identified by its name. Therefore, there is no concept of method overloading in C as there is in Java. There can be only one main( ) function in a C application. See the course coding standards for function naming conventions.See the course coding standards for function naming conventions.the course coding standardsthe course coding standards

3. Arguments vs Parameters A parameter is defined in the function definition. It is a place holder for the argument during function execution A parameter is defined in the function definition. It is a place holder for the argument during function execution void printInt( int n ) // n is the parameter { printf( “%20d\n”, n); } An argument is a value passed to a function when the function is called An argument is a value passed to a function when the function is called int age = 42; printInt( age );// age is the argument These terms are often (incorrectly) used interchangeably, but the context is usually clear These terms are often (incorrectly) used interchangeably, but the context is usually clear

4. Passing Arguments Primitive types (int, char, float, etc) and structs are passed to function “by value” Primitive types (int, char, float, etc) and structs are passed to function “by value” – A copy of the argument is passed to the function – Changing the parameter within the function has no effect on the argument in the calling code Arrays are passed “by reference” Arrays are passed “by reference” – A copy of the address of the array is passed to the function The parameter is an “alias” for the argument – References to array elements in the function refer to array elements in the calling code – Array parameters which are not intended to be changed by a function should be qualified as const

5. Passing Arguments /* ages.c */ #include void growOlder( int a[ ], int size) { int k; for (k = 0; k < size; k++) ++a[ k ]; } int avgAge( const int array[ ], int size) { int k, sum = 0; for (k = 0; k < size; k++) sum += array[ k ]; return sum / size; } int main( ) { int nrStudents = 6; int ages[ 6 ] = {19, 18, 17, 22, 44, 55}; growOlder( ages, nrStudents ); int avg = avgAge( ages, nrStudents ); printf(“The average age is %d\n”, avg); return 0; }

6. Auto Type Conversion As we’ve seen, the compiler can and will automatically convert a “small” data type to a “larger” data type without problems. As we’ve seen, the compiler can and will automatically convert a “small” data type to a “larger” data type without problems. char initial = ‘B’; short age = 42; int intAge = 42, intInitial = initial; long longAge = age; The same type conversion occurs for function arguments. The same type conversion occurs for function arguments. short myAge = 42, yourAge = 33; long max( long a, long b); long older = max ( myAge, yourAge);

7. Passing 2-D Arrays Passing a 2-d array to a function is similar to passing a 1-d array Passing a 2-d array to a function is similar to passing a 1-d array Basic function prototype Basic function prototype void printChessBoard( char [ 8 ][ 8 ] theBoard); Calling the function Calling the function char chessBoard[ 8 ] [ 8 ]; printChessBoard( chessBoard ); As we will see, the compiler needs to know the size of each row, but not the number of rows. This allows an alternative prototype As we will see, the compiler needs to know the size of each row, but not the number of rows. This allows an alternative prototype void printChessBoard( char[ ] [ 8 ] theBoard );

8. Recursion C functions may be called recursively.C functions may be called recursively. –Typically a function calls itself A properly written recursive function has the following propertiesA properly written recursive function has the following properties –A “base case” - a condition which does NOT make a recursive call because a simple solution exists –A recursive call with a condition (usually a parameter value) that is closer to the base case than the condition (parameter value) of the current function call Each invocation of the function gets its own set of arguments and local variablesEach invocation of the function gets its own set of arguments and local variables We’ll see how recursion is implemented laterWe’ll see how recursion is implemented later

9. Recursion Example /* print an integer in decimal ** K & R page 87 (may fail on largest negative int) */ #include void printd( int n ) { if ( n < 0 ) { printf( “-” ); n = -n; } if ( n / 10 )/* (n / 10 != 0) -- more than 1 digit */ printd( n / 10 );/* recursive call: n has 1 less digit */ printf( “%c”, n % 10 + ‘0’); /* base case --- 1 digit */ }

10. Recursive Exercise Complete the following recursive function that sums all of the integers from 1 to N int sumToN( int N ) { if (____________________) // base case return N; else// recursive call return ______________________; }

11. Inline Functions C99 onlyC99 only Short functions may be defined as “”. This is a suggestion to the compiler that calls to the function should be replaced by the body of the function.Short functions may be defined as “ inline ”. This is a suggestion to the compiler that calls to the function should be replaced by the body of the function. functions provide code structure and readability and (may) increase performanceinline functions provide code structure and readability and (may) increase performance inline bool isEven( int n ) { return n % 2 == 0; } inline max( int a, int b ) { return a > b ? a : b; }

12. Macros C provides macros as an alternative to small functions.C provides macros as an alternative to small functions. More common prior to C99 (inline functions are better)More common prior to C99 (inline functions are better) Handled by the preprocessorHandled by the preprocessor Several “gotcha”sSeveral “gotcha”s Parameters have no type.Parameters have no type. OK if used carefullyOK if used carefully General macro format.General macro format. –#define NAME( params if any ) code here Note: there is NO space between the name and the left parenthesis See macros.cSee macros.c

13. SQUARE( ) A simple macro to square a variableA simple macro to square a variable –#define SQUARE( x ) x * x Like all #defines, the preprocessor performs text substitution. Each occurrence of the parameter is replaced by the argument text.Like all #defines, the preprocessor performs text substitution. Each occurrence of the parameter is replaced by the argument text. int y = 5; int z = SQUARE( y ); But now consider this statementBut now consider this statement int w = SQUARE( y + 1 );

14. A better SQUARE( ) This version is betterThis version is better –#define SQUARE( x ) ( (x) * (x) ) int y = 5; int z = SQUARE( y ); int w = SQUARE( y + 1 ); But still doesn’t work in every caseBut still doesn’t work in every case int k = SQUARE( ++y );