C programming session 02

In this session, you will learn to: Work with operators Use loops Use formatted input-output functions Objectives

An operator: Is a symbol used to command the computer to do mathematical or logical manipulations. Operates on data and variables. C has a rich set of operators, which can be classified into following various categories: Relational operators Logical operators Unary operators Binary operators Ternary operator Compound assignment operators Increment/Decrement operators Working with Operators

Notations for logical operators in C are: Operator Notation OR | | AND && NOT ! Operator precedence: NOT (!) is evaluated before AND (&&), which is evaluated before OR (||). Brackets () are used to change this order. Logical Operators

Write a function that accepts either y or n only as input. For any other character input, an appropriate error message should be displayed and the input is accepted again. Practice: 2.1

Solution: #include<stdio.h> main() { char yn; do { puts(“Enter y/n (Yes/No)”); yn=getchar (); fflush (stdin); if(yn!=’y’ && yn!=’n’) puts(“Invalid input”); } while(yn!=’y’ && yn!=’n’); } Practice: 2.1 (Contd.)

Unary Operators: Operates on a single operand. Prefixed to an integer constant. Tells the compiler to reverse the sign by subtracting the value (or variable) from zero. Has the same effect as the – sign, which is used to indicate a number less than zero, for example -12. Unary Operators

Which of the following are valid? 1. valuea=-12; /* valuea is int* / 2. valuea = - valueb – 12 /* valuea and valueb both are int */ Practice: 2.2

Solution: 1. Valid 2. Valid Practice: 2.2 (Contd.)

Binary Operators: Operate on two operands. Are as follows: + (add) - (subtract) * (multiply) / (divide) % (modulo) Binary Operators

In the following set of statements: char ch; ch=’S’; ch=ch+’a’-‘A’; /*statement A*/ ch=ch+’A’-‘a’; /*statement B*/ What will be the value of ch after: 1. Statement A is executed? 2. Statement B is executed? Practice: 2.3

Solution: 1. ch is equal to s . Note that ‘a’-‘A’ gives 32 after statement 1 is executed. 2. ch is back to S after statement 2 is executed. Practice: 2.3 (Contd.)

There are some set or rules, if followed, would prevent unexpected results, at the time of execution of programs: Any operand of type char is converted to int . All floats are converted to doubles. If either operand is double , the other is converted to a double , giving a double result. Binary Operators (Contd.)

In which of the following assignments is there no loss of data? ( i is an int , f a float , and d a double ) i=d; d=f; f=d; i=f+d; d=i+f; Is type casting necessary in the following example? int i,j; float f; double d; d=f+(float) i + j ; Practice: 2.4

Solution: a. Loss of data. int set equal to a double. b. No loss of data. double set equal to a float . c. Loss of data. float set equal to a double . d. Loss of data. Right-hand result is a double while left-hand side is just an int . e. No loss of data. Right-hand result is a double and left-hand side is also a double . 2. Not necessary. The ints will automatically be converted to doubles (following the conversion of the float to a double ). Practice: 2.4 (Contd.)

Ternary Operator: Is a shorthand method for writing if.else conditional construct. Helps in reducing lines of code. Has the following form for the expression using the ternary operator: (test-expression) ? T-expression : F-expression; Ternary Operator

Consider the following example: if(condition) { Statements if condition is true } else { Statements if condition is false } Can be rewritten using the shorthand operator as follows: larger_of_the_two = ( x > y ) ? x : y; Ternary Operator (Contd.)

1. State whether True or False: In the general form of an expression that uses a ternary operator, the test expression will be checked. If it is true, the T-expression will be evaluated, otherwise the F-expression will be evaluated. 2. What will the following statement do? quotient = (b==0) ? 0 : (a/b); /*a, b, and quotient are ints*/ 3. Can the preceding statement be written as follows? quotient = (b) ? (a/b) : 0; 4. What will the following statement do? always_negative = (j>0) ? j : (-j); Practice: 2.5

Solution: True. If b is non-zero, it will determine the quotient of a and b . If b equals zero, quotient is set to 0. Yes. Note that if b is non-zero, the test expression ( b ) evaluates to true and hence quotient is set to ( a/b ). The variable always_negative will always take on a non-negative value, i.e. it will be assigned the absolute value of j . The name of the variable always_negative is just a red herring. Remember that self-documenting variable names will help in writing programs that are readable. Note the unary operator ( -j ). Practice: 2.5 (Contd.)

Compound Assignment Operators: Are useful especially when long variable names are used. Has the following general form: left-value op= right-expression; Here op can be either + (add), - (subtract, * (multiply), / (divide), and % (modulo). Consider the following example: a_very_long_identifier=a_very_long_identifier + 2; It can be written as: a_very_long_identifier += 2; Compound Assignment Operators

Increment / Decrement Operators: Are used to increase or decrease the value of a variable by 1. Has the following two forms: The ++ (two plus symbols without a space), called the increment operator while that in ++ before the variable is called the pre increment operator and after the variable is called the post increment operator. The -- (two minus symbols without a space), called the decrement operator while that in ++ before the variable is called the pre decrement operator and after the variable is called the post increment operator. Increment / Decrement Operators

Consider the following code snippet: total = sum++; /* statement A */ total = ++sum; /* statement B */ The first statement is equivalent to: total = sum; sum = sum + 1; While the second is the same as: sum = sum + 1; total = sum; Increment / Decrement Operators (Contd.)

Consider the following code snippet: int sum = 3, total = 5; total = sum++; total = ++sum; /*statement A */ total = sum— total = --sum; /*statement B */ What will be the values of total and sum after: statement A is executed? statement B is executed? Practice: 2.6

State whether True or False: The following statement: for(i = 0; i< 100); i = i + 1) { Some statements } can be written as: for (i = 0; i < 100; i++) { Some statements } Practice: 2.6 (Contd.)

State whether True or False: The for statement in #2 can also be written as: fori = 0; i < 100; ++i)/*Note: ++i and not i++*/ { Some statements } 4. Write a program, which reads in a year and reports on whether it is a leap year or not (centuries should also be considered). Practice: 2.6 (Contd.)

Solution: total=5, sum=5 total=3, sum=3 quite a complicated way of reducing total by 2. 2. True. i+1 is equivalent to i++. True. i+1 is equivalent to 1+i. 4. Practice: 2.6 (Contd.)

The while and do…while looping constructs are generally used in situations where the number of execution of the loop is not known. The for loop construct is used when the number of execution of the loop is known. Using Loops

The for loop construct: Has three components in the loop control: Initialization Condition Re-initialization (increment/decrement) Has the following sequence of execution: Initialization Evaluation of loop condition Body of loop Re-initialization The for Loop Construct

The sequence of execution of a complete for loop construct is shown in the following figure. The for Loop Construct (Contd.) TRUE INITIALIZATION EVALUATE CONDITION BODY OF LOOP REINITIALIZATION FALSE

In a for loop construct: Multiple initializations and/or multiple re- initializations, are separated by commas. Multiple conditions are specified using logical operators. The for Loop Construct (Contd.)

Write a function to accept twenty characters from the character set, and to display whether the number of lower-case characters is greater than, less than, or equal to number of upper-case characters. Display an error message if the input is not an alphabet. Modify the function to accept characters endlessly until the character ! is input from keyboard. Practice: 2.7

Solution: 1. 2. Practice: 2.7 (Contd.)

At times there is a need to exit from a loop before the loop condition is re-evaluated after iteration. To exit from loop control, break and continue statements are used. Controlling the Loop Execution

Write a function, which accepts numbers until 0 is entered or 10 numbers have been accepted. The function prints the total number of entries, the number of positive entries, and the sum of all the positive numbers. Practice: 2.8

Solution: Practice: 2.8 (Contd.)

C provides the following functions for formatted input-output: printf() scanf() Using Formatted Input-Output Functions

Syntax of the formatted output function printf() is: printf (format, data1, data 2, ….); Consider the following example: printf(“%c”, inp); The character specified after % is called a conversion character. The conversion character allows one data type to be converted to another type and printed. Formatted Output

The conversion characters and their meanings are shown in the following table. Formatted Output (Contd.) Character Meaning d the data is converted to decimal (integer) c the data is taken as a character s the data is a string and characters from the string are printed until a NULL character is reached f the data is output as a double or float with a default precision to 6

What is the output of the statement: printf(“Integer is: %d; Alphabet is: %c\n”, inum, inp); where inum contains 15 and inp contains Z . Practice: 2.9

Solution: Integer is: 15; Alphabet is Z. Practice: 2.9 (Contd.)

The scanf() function is used for formatted input. The syntax for the scanf() functions is as follows: scanf (format, data1, data2……); Here format - The format-specification string data1, data2 - Data names where the input data is to be stored as per the format-specification string Formatted Input

The format-specification string in scanf() consists of: Blanks, tabs, (also called white space characters). New line which are ignored. Conversion consisting of %, an optional number specification specifying the width and a conversion character. While accepting strings using scanf() , a space is considered as a string terminator. Formatted Input (Contd.)

Practice: 2.10 Write a function to accept and display the element number and the weight of a Proton. The element number is an integer and weight is fractional.

Practice: 2.10 (Contd.) Solution: #include<stdio.h> main() { int e_num; float e_wt; printf(“Enter the Element No. and Weight of a Proton\n”); scanf(“%d %f”, &e_num, &e_wt); fflush(stdin); printf(“The Element No. is: “, e_num); printf(“The weight of a Proton is: %f\n“, e_wt); }

Practice: 2.11 Write a function to input a string of continuous characters with no white space as part of the input. The function should assign the input to variables of the types specified in the following table. The function should also print out each of the assigned data items in separate lines. Position of character from start of string Number of characters Type of argument to assign 1 2 int 3 4 float 7 2 char (string) 9 3 int

Practice: 2.11 Solution: #include<stdio.h> main() { int i,j; char str[3]; float fnum; printf(“Enter a string of 11 chrs\n”); /*why 11: because 11 is the total length of */ /*input.*/ scanf(“%2d %4f %2s %3d”,&i, &fnum, str, &j); fflush(stdin); printf(“%2d\n %4f\n %2s\n %3d\n”, i, fnum, str, j); }

In this session, you learned that: An operator is a symbol that is used to command the computer to do mathematical or logical manipulations. The operators in C language are classified into the following categories: Logical operators Unary operators Binary operators Ternary operator Compound assignment operators Increment/Decrement operators Summary

The logical operators of C and their notations are as follows. The unary operator prefixed to an integer constant or variable tells the compiler to reverse the sign by subtracting the value or variable from zero. Binary operators in C language are + (add), - (subtract), * (multiply), / (divide), and % (modulo). Ternary operator offers a shorthand way of writing the commonly used if…else construct. Summary (Contd.) Operator Notation OR || AND && NOT !

The syntax for using the ternary operator is: (test-expression) ? T-expression : F-expression; Compound assignment operators simplify the statements. Increment / Decrement operators are used to increment/decrement a variable by 1. A for loop is used when the number of execution of the loop is known. The components of a for loop construct are: initialization loop condition reinitialization (increment/decrement) Summary (Contd.)

The sequence of execution of a complete for loop is: initialization evaluation of the loop condition the body of the loop reinitialization The break and continue statements are used to exit from loop control. The break statement is used to exit from all loop constructs ( while , do...while , and for ) and switch...case statements. The continue statement is used to skip all subsequent instructions and brings the control back to the loop. The function printf() is used for formatted output to standard output based on a format specification. Summary (Contd.)

The syntax of the function printf() is: printf(format, datal, data 2,,..); The function scanf() is used for formatted input from standard input and provides many of the conversion facilities of the function printf() . The syntax of the function scanf() is: scanf (format, datal, data2, ...); Summary (Contd.)

C programming session 02

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