CECS 121 Midterm Review Presented by REACH (If you have not signed the attendance sheet, please do so now!)

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Parts of the Program #include main() { printf(“\nC you later\n”); system(“pause”); }

Parts of the Program

Program Statements Serve to control program execution and functionality. Must end with a semicolon(;) with the exception of:  Comments: /* */  Preprocessor Directives: #include or #define  Begin and end program identifiers: { }  Function definition beginnings: main()

The main{} function  Functions allow you to group program statements under one name  C is case-sensitive so main(), MAIN(), and Main() are all different  The main function is special because the values it returns are returned to the operating system  Most main functions in this course do not take or pass information to the operating system

Escape Sequences  Definition: Escape sequences are specially sequenced characters used to format output  \” Ex: printf(“\“This is quoted text \“ “); -> “This is quoted text”  \’ Ex: printf(“A single quote looks like \’ ”); -> A single quote looks like ‘  \* This is a comment block *\

Directives  #include  Using a directive to include a header file  stdio.h = st an d ard i nput o utput header file  stdlib.h = st an d ard lib rary of ‘system’ commands

Memory  A computer’s long-term memory is called nonvolatile memory and is generally associated with mass storage devices, such as hard disk drives (HDDs) or solid state drives (SSDs).  A computer’s short term memory is usually random-access memory (RAM), which is volatile memory. It clears all of its data when power is removed from the computer.

Data Types Data TypeDescriptionDeclarationExample IntegerWhole numbers, positive or negative int x =__;-3, 0, 3, 29 Floating- point number All numbers, positive or negative, decimals and fractions float x =__; , 0.00, CharacterRepresentations of integer values known as character codes char x = ‘__’; m, M, $ To declare a constant (read only) value: const int x = 20 const float PI = 3.14

Variable Types TYPESIZEVALUES bool1 bytetrue (1) or false (0) char1 byte‘a’ to‘z’, ‘A’ to ‘Z’, ‘0’ to ‘9’, space, tab, and so on int4 bytes-2,147,483,648 to 2,147,483,647 short2 bytes-32,768 to 32,767 long4 bytes-2,147,483,648 to 2,147,483,647 float4 bytes+ - (1.2 x 10^-38 to 3.4 x 10^38) double8 bytes+- (2.3 x 10^-308 to -1.7 x 10^308)

Printf() ; Scanf()  Can you explain what each line of the code is doing?

Conversion Specifiers  Character - %c  Integer - %d  Float (decimal)- %f  String - %s  Printf Format Tags: %[flags][width][.precision][length]specifier e.g. -> %[.precision]specifer -> %.2f

Conversion Specifier Examples: int main() { printf (“%c %c \n", 'a', 65); -> aA printf ("%010d \n", 1977); -> printf ("floats: %.2f \n", ); -> 3.14 printf ("floats: %.4f \n", ); -> printf ("%s \n", "A string"); -> A string printf(“%f \n”, 55.55); -> return 0; }

Review Printing with Precision ExamplePrintout printf(“%.1f”, );3.1 printf(“\n%.2f”, );3.12 printf(“\n%.3f”, );3.123 printf(“\n%.4f”, ); printf(“\n%.5f”, ); printf(“\n%.6f”, );

scanf()  Syntax scanf(“conversion specifier”, &variable); Conversion Specifiers Description %dReceives integer value %fReceives floating-point number %cReceives character Missing this is a common error!

Can you predict the printout when the user enters 2 and 4? #include main() { int iOperand1 = 0; int iOperand2 = 0; printf(“\n Enter first operand: “); scanf(“%d”, &iOperand1); printf(“\n Enter second operand: “); scanf(“%d”, &iOperand2); printf(“The result is %d \n”, 24/(iOperand1 * iOperand2)+6/3); }

Arithmetic and Order of Precedence OperatorDescription *Multiplication /Division %Modulus (remainder) +Addition -Subtraction Order of Precedence Description ( )Parentheses are evaluated first, from innermost to outermost *, /, %Evaluated second, from Left to Right +, -Evaluated last, from Left to Right

Can you predict the printout? #include main() { int x = 4; int y = 9; int result1, result2; result1 = y/x; result2 = y%x; printf(“The result is %d.%d \n”, result1, 25*result2); }

Conditions and Operators OperatorDescription ==Equal to !=Not Equal >Greater Than <Less Than >=Greater Than or Equal to <=Less Than or Equal to Order of Precedence Description &&AND condition ||OR condition

Boolean Operators Do you know the answers to these?  A. !( 1 || 0 )  B. !( 1 || 1 && 0 )  C. !( ( 1 || 0 ) && 0 )

Boolean Operators Quiz Answers  A. !( 1 || 0 ) ANSWER: 0  B. !( 1 || 1 && 0 ) ANSWER: 0 (AND is evaluated before OR)  C. !( ( 1 || 0 ) && 0 ) ANSWER: 1 (Parenthesis are useful!)

Conditional Statements

How Does This Code Work? #include int main() { int a; printf (“Enter one of the following: %d, %d, or %d\n”, 1, 2, 3); scanf(“%d”, &a); if(a==1|| a==2|| a ==3) { if(a==1) { printf(“\n %d is the loneliest number \n“, 1); } if(a==2) { printf(“\n%d is better than %d \n”,2,1); } if(a==3) { printf(“\n%d \’ s a crowd \n”,3); } else printf(“Sorry, you entered an invalid value\n”); }

Switch-Case Statements

Example Switch-Case Statement

The while(){} loop: while ( condition ) { //Code to execute while the condition is true } Example:

Do-While Loop  Syntax:  do { //Code executed while condition is true } while ( condition );  Question: What is the main difference between the “do-while” and “while” functions?

Operators Cont. x++;Tells the function to use the current value of x and increment it by 1. ++x;Increment the value of x by 1 and use the new value for calculations. x--; Tells the function to use the current value of x and decrease its value by 1. --x; Decrease the value of x by 1 and use the new value for calculations. e.g. x=0; printf(“The Value of x is: %d”, x++); printf(“\n The Value of x is: %d”,++x); Would results in:The Value of x is: 0 The Value of x is: 2 Application of: += & -=Equivalent Equation x += y; x = x + y; x -= y; x = x – y;

For Loop  Often used when the # of iterations is already known.  Contains 3 separate expressions: 1. Variable initialization 2. Conditional expression 3. Increment/Decrement Don’t forget: When writing a for loop, the “arguments” are separated by semicolons, not commas! i.e.… Do this: for(x=0 ; x<10 ; x++){ } Not this: for(x=0, x<10, x++){ }

For Loop example: This program uses a for(){} loop to count down from 10 to 0: #include main() { int x=0; for(x=10; x>=0; x--) { printf("%d \n", x); } return 0; }

Break/Continue Statements  break; Used to exit a loop. Once this statement is executed, the program will execute the statement immediately following the end of the loop.  continue; Used to manipulate program flow in a loop. When executed, any remaining statements in the loop will be skipped and the next iteration of the loop will begin

Function Prototypes & Definitions  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?

Calling Functions #include int mult(int, int); int main() { int x; int y; printf( "Please input the first number to be multiplied: " ); scanf( "%d", &x ); printf( “\nNow the second one: “); scanf( "%d", &y ); printf( “\nThe product of your two numbers is %d\n", mult( x, y ) ); getchar(); } int mult (int a, int b) { return a * b; }

Can you spot the errors? #include printNumber(); main() { int x; printNumber(x); } printNumber() { printf(“\n The number is %d \n”, x) }

Answer #include void printNumber( int x); main() { int x; printNumber(x); } void printNumber(int y) { printf(“\n The number is %d \n”, y); } *Note: it’s not absolutely necessary to write VOID, but it’s a good practice.

Variable Scope  Variable scope defines the lifetime of a variable  Local Scope: defined within functions and loses scope after function is finished. Can reuse in other functions  Global Scope: defined outside of functions and can be accessed by multiple functions

Can You Pick Out the Local and Global Variables? #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); }

More example code: #include int addNumbers(int, int, int, int); int multNumbers(int, int, int, int); main() { int a, b, c, d, counter=0; while( counter<6 ) { printf(“\n Please enter 4 integers separated by spaces:\n”); scanf(“%d %d %d %d”, &a, &b, &c, &d); printf(“\n %d \n”, addNumbers(a,b,c,d)-multNumbers(a,b,c,d)); count++; } int addNumbers(int f, int g, int h, int y) { return f+g+h+y; } int multNumbers(int f, int g, int h, int y) { return f*g*h*y; }

How to Declare a One- Dimensional Array  Can you declare a one-dimensional array made up of 10 integers?  Answer: int iArray[10]  Example array declarations -  int iArray[10];  float fAverages[30];  double dResults[3];  short sSalaries [9];  char cName[19]; (this makes 18 characters plus 1 null character)

Initializing 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()

Example of Initializing an Array Using a For() Loop #include main() { int x; int iArray[5]; for( x=0; x < 5 ; x++) { iArray[x] = 0; } ***N.B. to initialize the array, you give its size (in this case, five), but to access a specifc element, you use its index number, which always ascends from zero (In this case, the available cells are 0, 1, 2, 3, and 4).

Printing Arrays  Can you add code to this program so that it prints out the values of the array? #include main() { int x; int iArray[5]; for( x=0; x < 5 ; x++) { iArray[x] = 0; }

Answer #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]); }

Searching an Array: #include main() { int x, iValue, 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”); }

On the test… Some types of problems you will encounter:  True/False questions  Fill-in-the-blanks questions  Finding errors in programs Common mistakes on this test:  Not appending lines of code with a semicolon (“;”)  Forgetting to use semicolons when writing a FOR loop  Forgetting to add an ampersand (“&”) to your variable parameter in SCANF functions (and mistakenly using the ampersand when using PRINTF)  Off-by-one errors when accessing an array, especially when using a FOR loop.

 Avoid Extensive Study  Only Do a Brief Review  Do Something Relaxing  Get Plenty of Sleep  Avoid Stress-Producing Situations  Maintain a Positive Attitude Test Success: The Night Before The Test

 Get Off to a Good Start  Arrive on Time  Compose Yourself  Do a Final Scan of Your Notes  Maintain a Confident Attitude Test Success: The Day of the Test

Good luck from REACH on your test! (If you have not signed in, please do so before you leave!) Any Questions?