ECET 264 C Programming Language with Applications. C Program Control

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1 ECET 264 C Programming Language with Applications Lecture 7 C Program Control Paul I. Lin Professor of Electrical & Computer Engineering Technology Lecture 7 - Paul I. Lin 1 Lecture 7 C Program Controls Common Programming Errors: Syntax Errors, Logic Errors, Run-time Errors, and Undetected Errors C Program Control Structures Repetition Statements For Statement Do While Repetition Statement Selection Statements Switch multiple selection statement Break Continue Lecture 7 - Paul I. Lin 2 1

2 Lecture 7 C Program Controls C Programming Examples Example 7-1: Interest Calculation Example 7-2: ASCII Number Generation Example 7-3: Read Keyboard Inputs and Echo them on to the Monitor Screen Example 7-4: Generating 10 Random Numbers Example 7-5: Generating Seeded and Unseeded Random Numbers Example 7-6: Counting the Number of a, b, and c characters in a text file Example 7-7: A Calculator Program Lecture 7 - Paul I. Lin 3 Common Programming Errors Syntax errors Grammatical errors, such as misspelling or incorrect punctuation Can be caught by the compiler Logic errors (Caused as a result of faulty program design) Program logical errors Misuse operators, such as ==, = Program does not terminate properly or an endless loop Errors caused by inappropriate end of data Run-time errors (Errors occur during the execution of a program) Other undetected errors (Fail to perform its intended task; incorrect results) Lecture 7 - Paul I. Lin 4 2

3 Repetition Essentials Repetition is a group of statements the computer executes repeatedly while the condition remains true Counter Controlled repetition (definite repetition) A control variable (or loop counter) A proper initial value for the control variable The increment (or decrement) by which the control variable is modified each time through the loop Testing final value of the control variable to know when to end the loop Lecture 7 - Paul I. Lin 5 Repetition Essentials (cont.) Sentinel Controlled repetition (indefinite repetition) The precise number of repetitions is not known in advance The loop includes statement(s) that obtain ending condition data each time the loop is performed The ending condition is determined through a distinct input data called sentinel value which indicates end of data Lecture 7 - Paul I. Lin 6 3

4 Repetition Structures A loop is a form of repetition in which a sequence of statements is repeated a number of times. Repetition structures: are to take actions until the condition fails. while for do while Lecture 7 - Paul I. Lin 7 while Loop Repetition Structures (cont.) Control variables used in the loop control testing must be initialized Testing for the termination condition is done at the top of the while() loop while (1) endless loop which is equivalent to #define true 1 while(true). or for ( ; ; ). Lecture 7 - Paul I. Lin 8 4

5 for Loop for statement is a repetition statement provides a leading-test construct with initialization and re-initialization provisions for loop allows to repeat the statements for a fixed number of times Basic Format: for(initialization; end_cond_checking; update) s1; s2; sn; Lecture 7 - Paul I. Lin 9 for Loop (cont.) Form 1: Null Statement (can be used as a short time delay routine) for (i = 0; i< 10; i++) ; Form 2: Simple Statement for (i = 0; i < 10; i++) sum += 1; i =0 NO statement to be executed Loop continuation condition 10 is a final value of control variable ONE statement to be executed i< 10? False True sum += 1 i ++ Lecture 7 - Paul I. Lin 10 5

6 for Loop (cont.) Form 3: Compound Statement for (init; end_cond_checking; update) s1; s2; Form 4: Nested for Loops for ( ; ;) /* End Less Loop */ for (init; end_cond_checkig; update) s1; s2; s3; for (init; end_cond_checking; update) s4; More than ONE statement to be executed Include more then one FOR statement to be executed Lecture 7 - Paul I. Lin 11 Example 7 1 Interest Calculation This C program computes compound interest using the FOR loop. A person invests $ in a saving account yielding 3% of interest. Assuming that all interest is left on deposit in the account, calculate and print the amount of money in the account at the end of each year for 10 years using the following equation: a = p(1+r) n where p is the original amount invested r is the annual interest rate n is the number of year a is the amount on deposit at the end of the nth year Lecture 7 - Paul I. Lin 12 6

7 Example 7 1 (cont.) Interest Calculation /* Calculating compound interest*/ #include <stdio.h> #include <math.h> /* function main begins program execution */ int main() double amount; /* amount on deposit */ double principal = 500.0; /* starting principal */ double rate = 0.03; /* annual interest rate */ int year; /* year counter */ /* output table column head */ printf( "%4s%21s\n", "Year", "Amount on deposit" ); Lecture 7 - Paul I. Lin 13 Example 7 1 (cont.) Interest Calculation /* calculate amount on deposit for each of ten years */ for ( year = 1; year <= 10; year++ ) /* calculate new amount for specified year */ amount = principal * pow( rate, year ); /* output one table row */ printf( "%4d%21.2f\n", year, amount ); /* end for */ return 0; /* indicate program ended successfully */ Lecture 7 - Paul I. Lin 14 7

8 Example 7 1 (cont.) Interest Calculation Lecture 7 - Paul I. Lin 15 Example 7 2 ASCII Number Generation Write a C program to generate ASCII numbers (0 to 9) and display them as both decimal and hex number on the screen: %c -- the format specified reserves a default length of spaces for printing a character %d -- the format specified reserves a default length of spaces for printing a decimal number %x -- the format specified reserves a default length of spaces for printing a hex number Lecture 7 - Paul I. Lin 16 8

9 Example 7 2 (cont.) ASCII Number Generation #include <stdio.h> void main() char ascii; for (ascii = '0'; ascii <= '9'; ascii++) printf("ascii %c = Decimal %d = Hex %x \n", ascii, ascii, ascii); Lecture 7 - Paul I. Lin 17 Example 7 2 (cont.) ASCII Number Generation Output: ASCII 0 = Decimal 48 = Hex 30 ASCII 1 = Decimal 49 = Hex 31 ASCII 2 = Decimal 50 = Hex 32 ASCII 3 = Decimal 51 = Hex 33 ASCII 4 = Decimal 52 = Hex 34 ASCII 5 = Decimal 53 = Hex 35 ASCII 6 = Decimal 54 = Hex 36 ASCII 7 = Decimal 55 = Hex 37 ASCII 8 = Decimal 56 = Hex 38 ASCII 9 = Decimal 57 = Hex 39 Lecture 7 - Paul I. Lin 18 9

10 Example 7 3: Read Keyboard Input and Echo them on to Monitor Screen /* char0.c A simple for loop for controlling the activities of the keyboard input and screen output. */ #include <stdio.h> #define NEWLINE '\n' void main() char name[30]; int c; /*Execute following forever, CTRL C to stop*/ for(;;) printf("\nplease enter your name: "); gets(name); puts("is this your name?"); puts(name); printf("\nplease enter a digit: "); c = getchar(); puts("\nis this the digit?"); putchar(c); putchar(newline); fflush(stdin); /* Flush the keyboard buffer */ /* end of char0.c */ Lecture 7 - Paul I. Lin 19 Example 7 3: Read Keyboard Input and Echo them on Monitor Screen (cont.) Output: Please enter your name: Paul Lin Is this your name? Paul Lin Please enter a digit:2 Is this the digit? 2 Please enter your name: You entered Lecture 7 - Paul I. Lin 20 10

11 Example 7 4 Generating 10 Random Numbers /* This program seeds the random-number generator with the time, then displays 10 random integers */ #include <stdlib.h> #include <stdio.h> #include <time.h> int main( void ) int i; /* Seed the random-number generator with current time so that the numbers will be different every time we run the program. */ srand( (unsigned)time( NULL ) ); /* Display 10 numbers. */ for( i = 0; i < 10; i++ ) printf( " %6d\n", rand() ); Lecture 7 - Paul I. Lin 21 Example 7 4 (cont.) Generating 10 Random Numbers Sample Output: Lecture 7 - Paul I. Lin 22 11

12 Example 7 5: Generating Seeded and Unseeded Random Numbers /* randgen.c - Generating seeded and unseeded pseudo random numbers */ #include <stdio.h> #include <math.h> #include <stdlib.h> void main(void) int n; /* Generate 4 unseeded pseudo random numbers*/ for(n = 1; n < 5; n++) printf("%d\t", rand()); puts("\n"); /* Generate time() function seeded peudo random numbers */ srand((unsigned)time(null)); Lecture 7 - Paul I. Lin 23 Example 7 5: Generating Seeded and Unseeded Random Numbers (cont.) for(n = 1; n < 5; n++) printf("%d\t", rand()); puts("\n"); /* Reset peudo random generator */ srand(1); for(n = 1; n < 5; n++) printf("%d\t", rand()); puts("\n"); Lecture 7 - Paul I. Lin 24 12

13 Example 7 5: Generating Seeded and Unseeded Random Numbers (cont.) Lecture 7 - Paul I. Lin 25 Example 7 6: Counting the Number of a, b, and c Characters /* if0.c - Counting A, B, C characters */ #include <stdio.h> #define SIZE 81 #define FORMAT "A = %d, B = %d, C = %d\n" void main() int i; int a, b, c; // counters char ch, s[size]; a = b = c = 0; Lecture 7 - Paul I. Lin 26 13

14 Example 7 6: Counting the Number of a, b, and c Characters (cont.) for(;;) // Run forever; Enter <Ctrl C> to exit puts("enter a string"); gets(s); for(i = 0; (ch = s[i])!= '\0'; i++) if((ch == 'A') (ch == 'a')) a++; if((ch == 'B') (ch == 'b')) b++; if((ch == 'C') (ch == 'c')) c++; printf(format, a, b, c); Lecture 7 - Paul I. Lin 27 Example 7 6: Counting the Number of a, b, and c Characters (cont.) Output: You entered Enter a string The C Programming Language A = 3, B = 0, C = 1 Enter a string Lecture 7 - Paul I. Lin 28 14

15 do while while loop tests for the termination condition at the top of the while() loop before the body of the loop performed do while loop always executes its loop body at least once before testing the termination conditions do while loop is good to perform counting, adding, searching, sorting, monitoring, etc Lecture 7 - Paul I. Lin 29 do while (cont.) Syntax: Form 1: Simple Statement do statement; while (condition); Form 2: Compound Statements do s1; s2; s3; while (condition); Lecture 7 - Paul I. Lin 30 15

16 do while (cont.) Using Relational and Logical operators for Checking Ending Condition: do.. while(1) /* Endless loop */ do.. while(a > b) /* a greater than b */ do.. while(a <= b) /* a less or greater than b */ do.. while(a!= b) /* a not eaual to b */ do.. while(a == b) /* a equal to b */ do.. while(a < (c + b)) /* a less than c + b */ do.. while(!a) /* while not a */ do.. while(a && b) /* while a and b are both nonzero or true */ do.. while(a b) /* while either a or b is nonzero or true */ Lecture 7 - Paul I. Lin 31 switch A multiple selection statement Consists of a series of case labels, and optional default case Multi-way branch (a chain of if-else statement) To select among several different cases break is used to end each case to exit the switch The default case is optional Lecture 7 - Paul I. Lin 32 16

17 switch (cont.) General form of switch(n) Syntax: switch (n) case 1: statement 1; break; case n: statement n; break; default: statement; where n can only be an integer, unsigned integer, or character type variable Lecture 7 - Paul I. Lin 33 switch (cont.) Example: int j = 3; switch(j) case 1: printf( case 1 \n ); break; case 2: printf( case2 \n ); break; default: printf( case others \n ); break; Lecture 7 - Paul I. Lin 34 17

18 Example 7 7 A Calculator Program Problem Statement You are asked to write a C program that can be used as a calculator program. The requirement of this program is as follows: It will run under a DOS virtual machine using text based user interface. It will prompt the user to enter two numbers It then asks for one of the calculation: addition, subtraction, multiplication, or division The program calculates the result Displays answer and repeats the same calculation Analysis Three variables are required switch, case, multi-decision making is preferred Endless loop, Ctrl C to exit the loop Lecture 7 - Paul I. Lin 35 Example 7 7 A Calculator Program (cont.) /* switch0.c */ #include <stdio.h> #include <stdlib.h> void main() float n1, n2, result; char op[2]; while(1) /* Enter <Ctrl C> to exit */ fflush(stdin); puts("hit any key to continue, Ctrl C to exit\n"); getchar(); /* waiting for user to input */ printf("\nenter a number: "); scanf( %f, &n1); /* Console input */ printf("\nenter second number: "); scanf( %f, &n2); /* Console input */ Lecture 7 - Paul I. Lin 36 18

19 Example 7 7 A Calculator Program (cont.) printf("\nselect an operator +,-,*, x, / or \\: "); scanf( %s, op); switch(op[0]) case '+': result = n1 + n2; printf("%f\n", result); break; case '-': result = n1 - n2; printf("%f\n", result); break; case '*': case 'x': case 'X': result = n1 * n2; printf("%f\n", result); break; case '/': case '\\': result = n1 / n2; printf("%f\n", result); break; default: puts("wrong operator entered"); Lecture 7 - Paul I. Lin 37 Example 7 7 A Calculator Program (cont.) Output: Hit any key to continue Enter a number: 12.0 Enter second number: 20.0 Select an operator +,-,*, x, / or \: * Hit any key to continue Lecture 7 - Paul I. Lin 38 19

20 Summary Common Program Errors C Program Control More Repetition Statements For Statement Do While Repetition Statement More Selection Statements Switch multiple selection statement Next - Break and Continue statement Equality operator (==) and assignment operator (=) Lecture 7 - Paul I. Lin 39 Question? Answers lin@ipfw.edu Lecture 7 - Paul I. Lin 40 20

ECET 264 C Programming Language with Applications

ECET 264 C Programming Language with Applications Lecture 6 Control Structures and More Operators Paul I. Lin Professor of Electrical & Computer Engineering Technology http://www.etcs.ipfw.edu/~lin Lecture