REACH TEST REVIEW

1. CECS 121 EXAM 2 REACH TEST REVIEW

2. Function Prototypes & Definitions • Function Prototype Syntax return-type function_name ( arg_type arg1, ..., arg_typeargN); • 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?

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

4. Calling Functions • #include <stdio.h> • int mult ( int, int ); • main() { • int x,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(); // To pause the screen, same like system(“pause”) • } • int mult (int x, int y) // Make sure not to end this with a semicolon • { • return(x * y); • }

5. Calling Functions • #include <stdio.h> • void print_char( char *, int); • main() { • char name[20]=“REACH CRC”; • print_char(name, 3); // The name of the array is a pointer to that array • getchar(); • } • void print_char (char *nameStringArray, int x) • { • printf(“The character specified is: %c”, nameStringArray[x-1]); • }

6. What’s Wrong with This Code? • #include <stdio.h> • void printReportHeader(); • main() • { • printReportHeader; • } • void printReportHeader() • { • printf(“\n Column1\tColumn2\tColumn3\tColumn4 \n”); • }

7. What’s Wrong with This Code? • #include <stdio.h> • void printReportHeader(); • main() • { • printReportHeader; // Should be corrected to printReportHeader() • } • void printReportHeader() • { • printf(“\n Column1\tColumn2\tColumn3\tColumn4 \n”); • }

8. Variable Scope • 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

9. Can You Pick Out the Local and Global Variables? • #include <stdio.h> • void printNumbers(); • int iNumber; // This is a global variable reachable from any place in code • 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); • }

10. How to Declare a One-Dimensional Array • Can you declare a one-dimensional array made up of 10 integers? • data_type name[size_of_array] • Answer: intiArray[10]; • How to declare an Array • intiArray[10]; // Array of 10 integers • float fAverages[30];// Array of 10 floats • char cName[19];// 18 characters and 1 null character

11. How to Initialize a 1-D Array • 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()

12. Example of Initializing an Array Using a For() Loop • #include <stdio.h> • main() • { • int x; • intiArray[5]; • for( x=0; x < 5 ; x++) • { • iArray[x] = 0; • } • }

13. Printing Arrays • Can you add code that will print out the value of each element of iArray? • #include <stdio.h> • main() • { • int x; • int iArray[5]; • for( x=0; x < 5 ; x++) • { • iArray[x] = 0; • } • }

14. Answer • #include <stdio.h> • 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]); • } • }

15. Accessing the elements in an array • How do you search through an array?

16. #include <stdio.h> • 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”); • }

17. 2-D Arrays • 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]);

18. 2-D Arrays • Initializing: Use a second, nested FOR() loop • #include <stdio.h> • 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; • } • } • }

19. 2-D Arrays • Passing to a function: • #include <stdio.h> • #include<stdlib.h> • 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

20. POINTERS • Pointers are variables that contain memoryaddresses 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!

21. POINTERS • Examples of pointer declarations: FILE *fptr; //fptr is a pointer to a file int *a; //a is a pointer to a file float *b; //b is a pointer to a file char *c; //c is a pointer to a file • 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.

22. POINTERS • Consider the statements: #include <stdio.h> 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; } Winter Quarter

23. Use of (&) and (*) • 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 Winter Quarter

24. Pointers and Functions • 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. Winter Quarter

25. Pointers • 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

26. #include <stdio.h> 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 Pointers with Functions (example)

27. Const Pointers • To avoid accidently changing the value the pointer points to: Use const void custom(const int *); main(){} void custom(const int *) { }

28. Strings • 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”;

29. Declaring Strings & Size • 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

30. Manipulating Strings

31. String strlen() Example #include <stdio.h> #include<stdlib.h> #include <string.h> 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.

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

33. Strcpy() Example #include <stdio.h> #include <string.h> 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

34. Strcat() Example #include <stdio.h> #include <string.h> 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.

35. Strcmp() Example #include <stdio.h> #include <string.h> 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!

36. Strstr() Example (Find/Replace) /*This example searches for the "simple" substring in str and replaces that word for "sample".*/ #include <stdio.h> #include <string.h> 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

37. Quiz? 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.

38. Answer #include<stdio.h> 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 printf(“%d\n”,array[i]); for(i=0;i<10;i++) for(j=0;j<10;j++) { if(array[i]<array[j]) /* This will do Ascending order, if you need Descending order just flip the < to > */ { 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 printf(“%5d “,array[i]); getchar(); return 0; }

39. Quiz? • 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.

40. Answer #include<stdio.h> 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++) printf(“%d\n”,array[i]); sortArray(array,10); for(i=0;i<10;i++) printf(“%5d”,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)

41. Questions? • Good Luck from REACH in your Test.

42. References • TEXTBOOK RESOURCE: C Programming for the Absolute Beginner 2nd Edition by Michael Vine • www.cprogramming.com