CECS 121 EXAM 2

 Function Prototype Syntax return-type function_name ( arg_type arg1,..., arg_type argN);  Function Prototypes tell you the data type returned by the function, the data type of parameters, how many parameters, and the order of parameters  Function definitions implement the function prototype  Where are function prototypes located in the program?  Where do you find function definitions?

 Function Prototypes are placed after preprocessor directives and before the main(){} function.  Function Definitions are self contained outside of the main(){} function

#include int mult ( int x, int y ); main() { int x; int y; printf( "Please input two numbers to be multiplied: " ); scanf( "%d", &x ); scanf( "%d", &y ); printf( "The product of your two numbers is %d\n", mult( x, y ) ); getchar(); } int mult (int x, int y) { return(x * y); }

#include void print_char( char *, int); main() { char name[20]=“REACH CRC”; print_char(name, 3); getchar(); } void print_char (char *name, int x) { printf(“The character specified is: %c”, name[x-1]); }

#include void printReportHeader(); main() { printReportHeader; } void printReportHeader() { printf(“\n Column1\tColumn2\tColumn3\tColumn4 \n”) }

 Variable scope defines the life time of a variable  Local Scope: defined within functions and loses scope after function is finished. Can reuse in other functions (ex. p.123)  Global Scope: defined outside of functions and can be accessed by multiple functions

#include void printNumbers(); int iNumber; main() { int x; for(x=0, x<10,x++){ printf(“\n Enter a number:”); scanf(“%d”, &iNumber); printNumbers(); } void printNumbers() { printf(“\n Your number is: %d \n”, iNumber); }

 Can you declare a one-dimensional array made up of 10 integers?  data_type name[size_of_array]  Answer: int iArray[10];  How to declare an Array  int iArray[10];  float fAverages[30];  char cName[19]; 18 characters and 1 null character

 Why do we initialize? Because memory spaces may not be cleared from previous values when arrays are created  Can initialize an array directly  Example int iArray[5]={0,1,2,3,4};  Can initialize an array with a loop such as FOR()

#include main() { int x; int iArray[5]; for( x=0; x < 5 ; x++) { iArray[x] = 0; }

 Can you add code that will print out the value of each element of iArray? #include main() { int x; int iArray[5]; for( x=0; x < 5 ; x++) { iArray[x] = 0; }

#include main() { int x; int iArray[5]; for( x=0; x < 5 ; x++) { iArray[x] = 0; } for(x=0 ; x<5; x++) { printf(“\n The value of iArray index %d is %d \n”, x, iArray[x]); }

 How do you search through an array?

#include main() { int x; int iValue; int iFound = -1; int iArray[5]; for( x=0; x < 5 ; x++) iArray[x] = (x+x); printf(“\n Enter value to search for:”); scanf(“%d”, &iValue); for(x=0 ; x<5; x++) { if( iArray[x] ==iValue){ iFound =x; break; ) } if(iFound >-1) printf(“\n I found your search value in element %d \n”, iFound); else printf(“\n Sorry, your search value was not found \n”); }

 Declaring:  data_type name[size_dim_1][size_dim_2] ▪ size_dim_1 is known as “ROW” count. ▪ size_dim_2 is known as “COLUMN” count.  int double_array[20][10]  Accessing:  printf(“Element 2,5 is: %d”, double_array[2][5]);

 Initializing: Use a second, nested FOR() loop #include main() { int x, y, double_array[10][20]; for( x=0; x < 10 ; x++) // Outer loop goes with ROW count { for(y=0 ; y<20; y++) // Inner loop goes with Column count { double_array[x][y] = 0; }

 Passing to a function: #include void custom_func(int [][2]);// Multi dimensional arrays must have a bound main() { int double_array[2][2]={{1,2},{3,4}}; custom_func (double_array); system(“pause”); } void custom_func (int temp[][2]) { printf(“Test: %d, %d, %d”, temp[0][0],temp[0][1],temp[1][1]); } OUTPUT: Test: 1, 2, 4

Lect 14P. 19  Pointers are variables that contain memory addresses as their values.  A variable name directly references a value.  A pointer indirectly references a value. Referencing a value through a pointer is called indirection.  A pointer variable must be declared before it can be used.  ALL Arrays are Pointers!

Lect 14P. 20  Examples of pointer declarations: FILE *fptr; int *a; float *b; char *c;  The asterisk, when used as above in the declaration, tells the compiler that the variable is to be a pointer, and the type of data that the pointer points to, but NOT the name of the variable pointed to.

Lect 14P. 21Winter Quarter  Consider the statements: #include int main ( ) { FILE *fptr1, *fptr2 ;/* Declare two file pointers */ int *aptr ;/* Declare a pointer to an int */ float *bptr ;/* Declare a pointer to a float */ int a ;/* Declare an int variable */ float b ;/* Declare a float variable */ return 0; }

Lect 14P. 22Winter Quarter  When is & used?  When is * used?  & -- "address operator" which gives or produces the memory address of a data variable  * -- "dereferencing operator" which provides the contents in the memory location specified by a pointer

Lect 14P. 23Winter Quarter  If instead of passing the values of the variables to the called function, we pass their addresses, so that the called function can change the values stored in the calling routine. This is known as "call by reference" since we are referencing the variables.  The following shows a swap function modified from a "call by value" to a "call by reference". Note that the values are now actually swapped when the control is returned to main function.

 Unary operator (&) – “Address of” int x=10; int *xptr; xptr = &x; //xptr now points to x  Indirection operator (*) int x, y = 10; int *xptr; xptr = &y; x = *xptr //copies contents of y into x

Lect 14P. 25 #include void swap ( int *, int *) ; int main ( ) { int a = 5, b = 6; printf("a=%d b=%d\n",a,b) ; swap (&a, &b) ; printf("a=%d b=%d\n",a,b) ; return 0 ; } void swap( int *a, int *b ) { int temp; temp= *a; *a= *b; *b = temp ; printf ("a=%d b=%d\n", *a, *b); } Output: a=5 b=6 //printed from main a=6 b=5 //printed from inside swap a=6 b=5 // printed from main after calling swap function

 To avoid accidently changing the value the pointer points to: Use const void custom(const int *); main(){} void custom(const int *) { }

 Strings are character arrays that have a special set of functions for handling their data as complete sentences or “strings” of characters.  Since a string is an array it is also a pointer.  Character literals are expressed with a single quote: char example=‘a’;  String literals are expressed with double quote: char example[10]=“REACH”;

 When determining the maximum length your string variable needs to be it is important to consider a NULL Character: “\0” char example[10]=“REACH”; example[0] -> R example[1] -> E example[2] -> A example[3] -> C example[4] -> H example[5] -> \0

#include int main () { char szInput[256]; printf ("Enter a sentence: "); gets (szInput); printf ("The sentence entered is %u characters long.\n",(unsigned)strlen(szInput)); System(“pause”); return 0; } Output: Enter sentence: just testing The sentence entered is 12 characters long.

#include int main () { int i=0; char str[]="Test String.\n"; char c; while (str[i]) { c=str[i]; putchar (tolower(c)); i++; } return 0; } Output: test string. For toupper() will be same case, just replace tolower() by toupper()

#include int main () { char str1[]="Sample string"; char str2[40]; char str3[40]; strcpy (str2,str1); strcpy (str3,"copy successful"); printf ("str1: %s\nstr2: %s\nstr3: %s\n",str1,str2,str3); return 0; } Output: str1: Sample string str2: Sample string str3: copy successful

#include int main () { char str[80]; strcpy (str,"these "); strcat (str,"strings "); strcat (str,"are "); strcat (str,"concatenated."); puts (str); return 0; } Output: these strings are concatenated.

#include int main () { char szKey[] = "apple"; char szInput[80]; do { printf ("Guess my favourite fruit? "); gets (szInput); } while (strcmp (szKey,szInput) != 0); puts ("Correct answer!"); return 0; } Output: Guess my favourite fruit? orange Guess my favourite fruit? Apple Correct answer!

/*This example searches for the "simple" substring in str and replaces that word for "sample".*/ #include int main () { char str[] ="This is a simple string"; char * pch; pch = strstr (str,"simple") ; /* returns a pointer to first occurrence of “simple” in str*/ strncpy (pch,"sample",6); // copies 6 characters from source->pch puts (str); return 0; } Output: This is a sample string

Can you make a program to sort an array of 10 integers either ascending or descending order? Consider you have the array[10]={7,8,5,3,0,3,2,1,4,10} Write a code to do the sorting.

#include int main(){ int array[10]={7,8,5,3,0,3,2,1,4,10}; int temp=0,i,j; for(i=0;i<10;i++) // print the array before sorting cout<<array[i]<<" "; cout<<endl; for(i=0;i<10;i++) for(j=0;j<10;j++) { if(array[i] ” { temp=array[i]; // This will do the swapping array[i]=array[j]; array[j]=temp; } for(i=0;i<10;i++) // print the array after sorting cout<<array[i]<<" "; getchar(); return 0; }

 Can you modify the previous code to pass the array to a function that will sort the array and print the sorted array in main.

#include void sortArray(int [],int size); int array[10]={7,8,5,3,0,3,2,1,4,10};int temp=0,i,j; int main(){ for(i=0;i<10;i++) cout<<array[i]<<" "; cout<<endl; sortArray(array,10); for(i=0;i<10;i++) cout<<array[i]<<" "; getchar(); return 0; } void sortArray(int passedArray[],int arraySize) { for(i=0;i<arraySize;i++) for(j=0;j<arraySize;j++) { if(passedArray[i]<passedArray[j]) { temp=passedArray[i]; passedArray[i]=passedArray[j]; passedArray[j]=temp; } Calling the function sortArray(array,10) is equivalent to sortArray(&array[0],10)

 Good Luck from REACH in your Test.

 TEXTBOOK RESOURCE: C Programming for the Absolute Beginner 2 nd Edition by Michael Vine 