CSE1222: Lecture 7The Ohio State University1. logExample.cpp // example of log(k) for k =...
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Transcript of CSE1222: Lecture 7The Ohio State University1. logExample.cpp // example of log(k) for k =...
REPETITIVE STRUCTURES
CSE1222: Lecture 7 The Ohio State University 1
logExample.cpp// example of log(k) for k = 1,2,..,8. . .int main(){ cout << "log(1) = " << log(1.0) << endl; cout << "log(2) = " << log(2.0) << endl; cout << "log(3) = " << log(3.0) << endl; cout << "log(4) = " << log(4.0) << endl; cout << "log(5) = " << log(5.0) << endl; cout << "log(6) = " << log(6.0) << endl; cout << "log(7) = " << log(7.0) << endl; cout << "log(8) = " << log(8.0) << endl;
return 0;}
CSE1222: Lecture 7 The Ohio State University 2
logExample.cpp... cout << "log(1) = " << log(1.0) << endl; cout << "log(2) = " << log(2.0) << endl; cout << "log(3) = " << log(3.0) << endl; cout << "log(4) = " << log(4.0) << endl; cout << "log(5) = " << log(5.0) << endl; cout << "log(6) = " << log(6.0) << endl; cout << "log(7) = " << log(7.0) << endl; cout << "log(8) = " << log(8.0) << endl;...
> logExample.exelog(1) = 0log(2) = 0.693147log(3) = 1.09861log(4) = 1.38629log(5) = 1.60944log(6) = 1.79176log(7) = 1.94591log(8) = 2.07944
CSE1222: Lecture 7 The Ohio State University 3
Repetition Structures (Loops) Motivation:
If we want to repeat essentially the same code say 1000 times we should not have to write 100 lines of code!
We need a new statement to help us execute repetitive code
CSE1222: Lecture 7 The Ohio State University 4
logWhile.cpp// example of while loop for log(k) for k = 1,2,..,8. . .int main(){ int k(0);
k = 1; while (k <= 8) { cout << "log(" << k << ") = " << log(double(k)) << endl; k++; } return 0;}
CSE1222: Lecture 7 The Ohio State University 5
logWhile.cpp... k = 1; while (k <= 8) { cout << "log(" << k << ") = " << log(double(k)) << endl; k++; }...
> logWhile.exelog(1) = 0log(2) = 0.693147log(3) = 1.09861log(4) = 1.38629log(5) = 1.60944log(6) = 1.79176log(7) = 1.94591log(8) = 2.07944
CSE1222: Lecture 7 The Ohio State University 6
while Loops
The while statement syntax:
while (conditional expression){ statement1; statement2; ...}
CSE1222: Lecture 7 The Ohio State University 7
How while Loops Work1. First test the conditional expression
If it is true, then execute the statement(s)
within the loop structure is/are executed
2. After the statement(s) are executed, we try to repeat the process
If the condition is still true, then we will executethe statement(s) againThus, while the condition is true, keep repeating
3. If the condition ever evaluates to false, then stop the while statement; the program continues execution after the while statement
CSE1222: Lecture 7 The Ohio State University 8
Control Flow of a while Loop
TRUE
FALSE
Statement 1
Code after loop
Code prior to loop
Return tolooping condition
...
Condition is true?
CSE1222: Lecture 7 The Ohio State University 9
logWhile.cpp… while (k <= 8) { cout << "log(" << k << ") = " << log(double(k)) << endl; k++; } return 0;}
The variable k , which appears in the conditional expression, is called a loop variable
It is an important variable because its value determines whether the loop stops or keeps going
The condition is the most difficult part of writing a loop
CSE1222: Lecture 7 The Ohio State University 10
While Examplecount = 1;while (count <= 10){
cout << count << “ “;count++; //increment count!
}
Output is “1 2 3 4 5 6 7 8 9 10”
The behavior of the loop is determined by the loop variable(s): Initialization of the loop variable Use in the condition determines continuation or end of the loop Update of the loop variable
CSE1222: Lecture 7 The Ohio State University 11
Control Flow of the Example Program
TRUE
FALSE
coutcounter
Code after loop
counter = 1;
counter++
counter<= 10 ?
CSE1222: Lecture 7 The Ohio State University 12
Repetition Structures 2
Motivation 2:
Allow repetition of code based on input
For example, a program should be able to output n lines of cout statements where n is a user input
CSE1222: Lecture 7 The Ohio State University 13
logWhile2.cpp...int main(){ int n(0), k(0);
cout << "Enter number of logarithms to compute: "; cin >> n;
k = 1; while (k <= n) { cout << "log(" << k << ") = " << log(double(k)) << endl; k++; } return 0;}
CSE1222: Lecture 7 The Ohio State University 14
logWhile2.cpp... cout << "Enter number of logarithms to compute: "; cin >> n;
k = 1; while (k <= n) { cout << "log(" << k << ") = " << log(double(k)) << endl; k++; }...
> logWhile2.exeEnter number of logarithms to compute: 5log(1) = 0log(2) = 0.693147log(3) = 1.09861log(4) = 1.38629log(5) = 1.60944
CSE1222: Lecture 7 The Ohio State University 15
logWhile2.cpp... cout << "Enter number of logarithms to compute: "; cin >> n;
k = 1; while (k <= n) { cout << "log(" << k << ") = " << log(double(k)) << endl; k++; }...
What happens here?
> logWhile2.exeEnter number of logarithms to compute: -3
???
CSE1222: Lecture 7 The Ohio State University 16
Repetition Structures 3
If a program receives incorrect input, it can repeatedly prompt for the correct input
CSE1222: Lecture 7 The Ohio State University 17
logWhile3.cpp// example of while loop to prompt for correct input...int main(){ double x(0.0);
cout << "Enter number: "; cin >> x;
while (x <= 0) { cout << "Input must be positive." << endl; cout << "Enter number: "; cin >> x; } cout << "log(" << x << ") = “ << log(x) << endl; return 0;}
CSE1222: Lecture 7 The Ohio State University 18
logWhile3.cpp... cout << "Enter number: "; cin >> x;
while (x <= 0) { cout << "Input must be positive." << endl; cout << "Enter number: "; cin >> x; }
cout << "log(" << x << ") = " << log(x) << endl;...
> logWhile3.exeEnter number: -4.5Input must be positive.Enter number: 0Input must be positive.Enter number: 4.5log(4.5) = 1.50408
CSE1222: Lecture 7 The Ohio State University 19
logWhileError.cpp// example of a while loop with a logical error. . .int main(){ int k(0);
k = 1; while (k <= 8) { cout << "log(" << k << ") = " << log(double(k)) endl; }
return 0;}
CSE1222: Lecture 7 The Ohio State University 20
Try running this program
probability.cpp...int main(){ double p(0.0);
cout << "Enter probability player A wins 1 game: "; cin >> p;
while (p < 0.0 || p > 1.0) { cout << "Input must be in range [0:1]." << endl; cout << "Enter probability player A wins 1 game: "; cin >> p; }
cout << "Probability player A loses all 5 games = " << pow((1-p), 5.0) << endl;
return 0;}
CSE1222: Lecture 7 The Ohio State University 21
> probability.exeEnter probability player A wins: 2Input must be in range [0:1].Enter probability player A wins: -1Input must be in range [0:1].Enter probability player A wins: 0.2Probability player A loses all 5 games = 0.32768>
CSE1222: Lecture 7 The Ohio State University 22
...while (p < 0.0 || p > 1.0) { cout << "Input must be in range [0:1]." << endl; cout << "Enter probability player A wins 1 game: "; cin >> p; }...
temperature.cpp// print a table converting fahrenheit to celsius... int fahrenheit(0), min_fahrenheit(0), max_fahrenheit(0); int STEP_SIZE(10);
cout << "Enter min and max fahrenheit: "; cin >> min_fahrenheit >> max_fahrenheit;
fahrenheit = min_fahrenheit; // loop until fahrenheit is greater than max_fahrenheit while (fahrenheit <= max_fahrenheit) { // convert fahrenheit to celsius float celsius = (fahrenheit - 32.0) * 5.0/9.0;
cout << "farenheit = " << fahrenheit << “ celsius = " << celsius << endl;
fahrenheit += STEP_SIZE; // increment by STEP_SIZE }...
CSE1222: Lecture 7 The Ohio State University 23
temperature.cpp... int STEP_SIZE(10);... fahrenheit = min_fahrenheit; // loop until fahrenheit is greater than max_fahrenheit while (fahrenheit <= max_fahrenheit) { // convert fahrenheit to celsius float celsius = (fahrenheit - 32.0) * 5.0/9.0;
cout << "farenheit = " << fahrenheit << “ celsius = " << celsius << endl; fahrenheit += STEP_SIZE; // increment by STEP_SIZE }...
> temperature.exeEnter min and max fahrenheit: 20 60farenheit = 20 celsius = -6.66667farenheit = 30 celsius = -1.11111farenheit = 40 celsius = 4.44444farenheit = 50 celsius = 10farenheit = 60 celsius = 15.5556
CSE1222: Lecture 7 The Ohio State University 24
temperature.cpp... int STEP_SIZE(10);... fahrenheit = min_fahrenheit; // loop until fahrenheit is greater than max_fahrenheit while (fahrenheit <= max_fahrenheit) { // convert fahrenheit to celsius float celsius = (fahrenheit - 32.0) * 5.0/9.0;
cout << "farenheit = " << fahrenheit << “ celsius = " << celsius << endl; fahrenheit += STEP_SIZE; // increment by STEP_SIZE }...
> temperature.exeEnter min and max fahrenheit: 25 60farenheit = 25 celsius = -3.88889farenheit = 35 celsius = 1.66667farenheit = 45 celsius = 7.22222farenheit = 55 celsius = 12.7778
CSE1222: Lecture 7 The Ohio State University 25
temperature2.cpp...
int STEP_SIZE(5);... fahrenheit = min_fahrenheit; while (fahrenheit <= max_fahrenheit) { float celsius = (fahrenheit - 32.0) * 5.0/9.0; cout << "farenheit = " << fahrenheit << “ celsius = " << celsius << endl; fahrenheit += STEP_SIZE; // increment by STEP_SIZE }...
> temperature2.exeEnter min and max fahrenheit: 25 60farenheit = 25 celsius = -3.88889farenheit = 30 celsius = -1.11111farenheit = 35 celsius = 1.66667farenheit = 40 celsius = 4.44444farenheit = 45 celsius = 7.22222farenheit = 50 celsius = 10farenheit = 55 celsius = 12.7778farenheit = 60 celsius = 15.5556
CSE1222: Lecture 7 The Ohio State University 26
temperatureError.cpp// print a table converting fahrenheit to celsius... int fahrenheit(0), min_fahrenheit(0), max_fahrenheit(0); int STEP_SIZE(10);
cout << "Enter min and max fahrenheit: "; cin >> min_fahrenheit >> max_fahrenheit;
fahrenheit = min_fahrenheit; // loop until fahrenheit does not equal max_fahrenheit while (fahrenheit != max_fahrenheit) // Note != instead of <= { // convert fahrenheit to celsius float celsius = (fahrenheit - 32.0) * 5.0/9.0;
cout << "farenheit = " << fahrenheit << “ celsius = " << celsius << endl; fahrenheit += STEP_SIZE; // increment by STEP_SIZE }...
CSE1222: Lecture 7 The Ohio State University 27
sinWhile.cpp (Error)…int main(){ double x(0.0); double increment(0.1);
cout.setf(ios::fixed); while (x != 1.0) { cout << x << ": " << sin(x) << " " << cos(x) << endl; x += increment; }
return 0;}
CSE1222: Lecture 7 The Ohio State University 28
FOR LOOPS
CSE1222: Lecture 7 The Ohio State University 29
logFor.cpp// example of for loop for log(k) for k = 1,2,..,8
#include <iostream>#include <cmath>using namespace std;
int main(){ for (int k = 1; k <= 8; k++) { cout << "log(" << k << ") = " << log(double(k)) << endl; }
return 0;}
CSE1222: Lecture 7 The Ohio State University 30
logFor.cpp... for (int k = 1; k <= 8; k++) { cout << "log(" << k << ") = " << log(double(k)) << endl; }...
> logFor.exelog(1) = 0log(2) = 0.693147log(3) = 1.09861log(4) = 1.38629log(5) = 1.60944log(6) = 1.79176log(7) = 1.94591log(8) = 2.07944
CSE1222: Lecture 7 The Ohio State University 31
for Loop Syntax
for (initialize; condition; alter)
{statement1;statement2;statement3;statement4;...
}
CSE1222: Lecture 7 The Ohio State University 32
for Loop Syntax (2) Initializing list
A statement to set the starting value(s) of variables (normally a loop counter)
Expression The looping condition
Altering list Statement that is executed at the end of every loop traversal Normally determines how the counter is manipulated after each
pass through the loop
Important note: At the end of a pass through the loop, the statements in the altering list is executed BEFORE the loop expression is evaluated
CSE1222: Lecture 7 The Ohio State University 33
How for Loops Work1. First, the initialization statements are executed
2. Then the conditional expression is tested. If it is true, then the statement(s) within the loop structure is/are executed.
3. Once the end of those statements is reached, then altering statements are executed, and the process is repeated.
4. If the expression ever evaluates to false, then the loop statement is exited, and the program continues beyond the loop.
CSE1222: Lecture 7 The Ohio State University 34
Control Flow of a for Loop
TRUE
FALSE
Statement 1
Code after loop
InitializeStatement;
Return tolooping condition
...
Altering statement;
Code prior to loop
Condition is true?
CSE1222: Lecture 7 The Ohio State University 35
for Loop Example for (int k = 1; k <= 8; k++) { cout << "log(" << k << ") = " << log(double(k)) << endl; }
// the while-loop equivalent: int k(0); . . . k = 1; while (k <= 8) { cout << "log(" << k << ") = " << log(double(k)) << endl; k++; }
CSE1222: Lecture 7 The Ohio State University 36
for Loop Example2// Compute n logarithms:
for (int k = 1; k <= n; k++) { cout << "log(" << k << ") = " << log(double(k)) << endl; }
// the while-loop equivalent: int k(0); . . . k = 1; while (k <= n) { cout << "log(" << k << ") = " << log(double(k)) << endl; k++; }
CSE1222: Lecture 7 The Ohio State University 37
(Too) Clever for Loop Example double x(0.0); cout << “Enter Number: “; for (cin >> x; x <= 0; cin >> x) // a while loop is better { cout << "Input must be positive." << endl; cout << "Enter number: "; }
// the while-loop equivalent: double x(0.0); cout << “Enter number: “; cin >> x; while (x <= 0) { cout << "Input must be positive." << endl; cout << "Enter number: "; cin >> x; } cout << "log(" << x << ") = " << log(x) << endl;
CSE1222: Lecture 7 The Ohio State University 38
for Loops for loops and while loops are
interchangeable
A for loop is a pre-test loop
Whether to use a while or a for loop is a question of style and readability
Use for loops to count from a to bUse while loops to iterate until some condition is
satisfied
CSE1222: Lecture 7 The Ohio State University 39
for Loop Example4 for (int k = 1; k <= 8; k++) { cout << "log(" << k << ") = " << log(double(k)) << endl; } cout << k << endl; // SYNTAX ERROR
// Variable k can be declared before the for-loop int k(0); for (k = 1; k <= 8; k++) { cout << "log(" << k << ") = " << log(double(k)) << endl; } cout << k << endl; // What is the value of k?
CSE1222: Lecture 7 The Ohio State University 40
Using Nested Loops A loop inside of another loop Extremely useful and very common
for (int i = 1; i <= 5; i++){ cout << “i is now “ << i << endl;
//inner (nested) loop for (int j = 1; j <= 4; j++) {
cout << “j is now “ << j << endl; }
} //What is the output?
CSE1222: Lecture 7 The Ohio State University 41
TRUE
TRUE
FALSE
cout“i is now..”
Code after loop
int i = 1;
i++;
int j = 1;
cout“j is now..”
j++;
FALSE
i <= 5?
j <= 4?
CSE1222: Lecture 7 The Ohio State University 42
Nested for loops: square.cpp// print a square of x's... int length(0);
cout << "Enter square edge length: "; cin >> length;
for (int row = 1; row <= length; row++) { // print length x's for (int col = 1; col <= length; col++) { cout << "x"; } cout << endl; // print newline to finish row }...
CSE1222: Lecture 7 The Ohio State University 43
Nested for loops: square.cpp... for (int row = 1; row <= length; row++) { // print length x's for (int col = 1; col <= length; col++) { cout << "x"; } cout << endl; // print newline to finish row }...
> square.exeEnter square edge length: 6xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
CSE1222: Lecture 7 The Ohio State University 44
Nested for loops: diagonal.cpp// print a diagonal of x's... int length(0);
cout << "Enter diagonal length: "; cin >> length;
for (int row = 1; row <= length; row++) { // print (row-1) spaces for (int col = 1; col <= row-1; col++) { cout << " "; } cout << "x" << endl; // print x on diagonal }...
CSE1222: Lecture 7 The Ohio State University 45
Nested for loops: diagonal.cpp... for (int row = 1; row <= length; row++) { // print (row-1) spaces for (int col = 1; col <= row-1; col++) { cout << " "; } cout << "x" << endl; // print x on diagonal }...
> diagonal.exeEnter diagonal length: 6x x x x x x
CSE1222: Lecture 7 The Ohio State University 46
squareError.cpp// version of square.cpp with errors... int length(0);
cout << "Enter square edge length: "; cin >> length;
for (int row = 1; row <= length; row++); { // print length x's for (int col = 1; col <= length; col++); { cout << "x"; } cout << endl; // print newline to finish row }...
CSE1222: Lecture 7 The Ohio State University 47
do-while loops A do-while loop checks the condition at the
end of the loop
Example: char c(‘n’); do {
... //rest of the program cout << “Do you wish to continue: “;
cin >> c; } while (c == ‘y’ || c == ‘Y’);
See text for more details.
CSE1222: Lecture 7 The Ohio State University 48
Conclusion on Loops
Loops are generally used for repetition of a section of code
There are three basic types:while, for, and do-whilewhile and for are pretest (entrance
controlled)do-while is posttest (exit controlled)
CSE1222: Lecture 7 The Ohio State University 49
Common Programming Errors (1)
Use == when comparing for equivalence in while, for, and do-while statements!
(Same as using == in if-statements)
Precision problem: double x, y;. . . “while (x != y)” may always be true even
though mathematically x should equal y
CSE1222: Lecture 7 The Ohio State University 50
Common Programming Errors (1)For each statement, what is the output?
for (int i = 1; i < 7; i++) { cout << i << endl; }
for (int i = 1; i <= 7; i++) { cout << i << endl; }
for (int i = 0; i <= 7; i++){ cout << i << endl; }
for (int i = 0; i < 7; i++)
{ cout << i << endl; }
CSE1222: Lecture 7 The Ohio State University 51
Common Programming Errors (1)For each statement, what is the output?
for (int i = 1; i < 7; i++) { cout << i; }
for (int i = 1; i < 7; i++){
cout << “Row “ << i;for (int j = 1; j < 4; j++){ cout << “ Col “ << j << endl; }
}
CSE1222: Lecture 7 The Ohio State University 52
Common Programming Errors (2) Do not place a semicolon at the
end of a for statement:int i;for (i = 1; i <= 10; i++);{ cout << “i = “ << i << endl; }
What does this output?
CSE1222: Lecture 7 The Ohio State University 53
Common Programming Errors (3) Use semicolons, not commas, to separate
items in a for statement:for (i=0, i<10, i++) //invalidfor (i=0; i<10; i++) //valid
Do not forget the semicolon at the end of the while statement in a do-while loopdo {
...} while(x > 0);
CSE1222: Lecture 7 The Ohio State University 54
LOOP PROGRAMMING
TECHNIQUES
CSE1222: Lecture 7 The Ohio State University 55
Interactive Input with a loopint main(){
double x(0.0), total(0.0), average(0.0);const int NUM_INPUTS(4);
total = 0.0;for (int i = 0; i < NUM_INPUTS; i++){
// ask user for a numbercout << "Enter a number: ";cin >> x;
total = total + x;}
average = total / NUM_INPUTS;cout << "The average of the entered values is: "
<< average << endl;}
CSE1222: Lecture 7 The Ohio State University 56
Selection within a Loopint main(){
double x(0.0), postot(0.0), negtot(0.0);const int NUM_INPUTS(5);
// NOTE: postot and negtot initialized to 0.for (int i = 1; i <= NUM_INPUTS; i++){
cout << "Enter a number: ";cin >> x;
// Selection: Separate positive from negative inputs.if (x > 0)
{ postot = postot + x; }else
{ negtot = negtot + x; }}
cout << "The positive total is " << postot << endl;cout << "The negative total is " << negtot << endl;
return(0);}
CSE1222: Lecture 7 The Ohio State University 57
Selection within a Loop (2)int main(){
double x(0.0), postot(0.0), negtot(0.0);
cout << "Enter a number: ";cin >> x;
// NOTE: postot and negtot initialized to 0.while (x != 0.0){
// Selection: Separate positive from negative inputs.if (x > 0)
{ postot = postot + x; }else
{ negtot = negtot + x; }
cout << "Enter a number: ";cin >> x;
}
cout << "The positive total is " << postot << endl;cout << "The negative total is " << negtot << endl;
. . .
CSE1222: Lecture 7 The Ohio State University 58
Evaluating Functions of One Variable// Calculates several values for y = 10x² + 3x
- 2int main(){
int x(0), y(0), xmin(0), xmax(0);
cout << "Minimum and maximum x values: ";cin >> xmin >> xmax;
for (x = xmin; x <= xmax; x++){
y = 10 * pow(x, 2) + 3 * x – 2; cout << "x = " << x
<< " f(x) = " << y << endl; }
}
CSE1222: Lecture 7 The Ohio State University 59
Prompting for Correct Inputint main(){
const int MAX_AGE(125);int age(0);
cout << “Enter your age (1-“ << MAX_AGE << “):”;cin >> age;
while (age <= 0 || age > MAX_AGE){
cout << “Invalid input. Try again.” << endl;
cout << “Enter your age (1-“ << MAX_AGE << “):”;cin >> age;
}}
CSE1222: Lecture 7 The Ohio State University 60
Summation: Sum of Cubes...int main(){
long sum(0);int n(0);
cout << “Enter number of terms in the summation: “;cin >> n;
for (int i = 1; i <= n; i++) {
sum += i*i*i; }
cout << “1^3 + 2^3 + 3^3 + ... + “ << n << “^3 = “ << sum << endl;
return 0;}
CSE1222: Lecture 7 The Ohio State University 61
Summation Over Two Variables Input: n
Compute
CSE1222: Lecture 7 The Ohio State University 62
Summation Over Two Variables Compute
Table of (i-j) (where j ≤ i):
CSE1222: Lecture 7 The Ohio State University 63
(i-j) j=0 j=1 j=2 j=3 ...
i=0 0 ...
i=1 1 0 ...
i=2 2 1 0 ...
i=3 3 2 1 0 ...
... ... ... ... ... ...
Summation Over Two Variables
Input: n
Compute Algorithm:
1. sum ← 0;
2. for i ← 0 to n do
3. for j ← 0 to i do
4. sum ← sum + (i-j);
CSE1222: Lecture 7 The Ohio State University 64
Algorithm
From “Programming and Problem Solving with C++” By Nell Dale:
An algorithm is “a step-by-step procedure for solving a problem”.
CSE1222: Lecture 7 The Ohio State University 65
Summation Over Two Variables
Input: n
Compute Algorithm:
1. sum ← 0;
2. for i ← 0 to n do
3. for j ← 0 to i do
4. sum ← sum + (i-j);
CSE1222: Lecture 7 The Ohio State University 66
Summation over two variables...int main(){ long sum(0); // Initialize sum to zero int n(0);
cout << "Enter max value of i: "; cin >> n;
for (int i = 0; i <= n; i++) { for (int j = 0; j <= i; j++) { sum = sum + (i-j); } }
cout << "sum_{i=0}^n sum_{j=0}^i (i-j) = " << sum << endl;
return 0;}
CSE1222: Lecture 7 The Ohio State University 67
Printing a table using nested loops
Input: n
Output: Table of 1/(i-j)2 for i = 1,...,n and j = 1,...,n.
Don’t print anything when i = j. Why?
CSE1222: Lecture 7 The Ohio State University 68
Printing a table using nested loops
Input: n
Output: Table of 1/(i-j)2 for i = 1,...,n and j = 1,...,n.
Algorithm:
1. for i ← 1 to n do
2. for j ← 1 to n do
3. if (i ≠ j) print 1/(i-j)2
4. else print "******"
5. print newline; (Why?)
CSE1222: Lecture 7 The Ohio State University 69
Printing a table using nested loops...int main(){ int numRows(0); int diff(0);
cout << "Enter number of table rows: "; cin >> numRows;
cout.setf(ios::fixed); // fixed precision output
...
CSE1222: Lecture 7 The Ohio State University 70
Printing a table using nested loops...for (int i = 1; i <= numRows; i++) { for (int j = 1; j <= numRows; j++) { if (i != j) { diff = i-j; cout << " " << 1.0/(diff*diff); } else { cout << " ****** "; } } cout << endl; // end row }...
CSE1222: Lecture 7 The Ohio State University 71
> printTable.exeEnter number of table rows: 6 ****** 1.000000 0.250000 0.111111 0.062500 0.040000 1.000000 ****** 1.000000 0.250000 0.111111 0.062500 0.250000 1.000000 ****** 1.000000 0.250000 0.111111 0.111111 0.250000 1.000000 ****** 1.000000 0.250000 0.062500 0.111111 0.250000 1.000000 ****** 1.000000 0.040000 0.062500 0.111111 0.250000 1.000000 ****** >
CSE1222: Lecture 7 The Ohio State University 72
for (int i = 1; i <= numRows; i++){ for (int j = 1; j <= numRows; j++) { if (i != j) { diff = i-j; cout << " " << 1.0/(diff*diff); } else { cout << " ****** "; } } cout << endl; // end row }
Problem: Print primes
Print prime numbers between 2 and n.
CSE1222: Lecture 7 The Ohio State University 73
Print prime numbers
Input: n
Output: Prime numbers between 2 and n.
Algorithm:
1. for k ← 2 to n do
2. flag_composite ← false;
3. for j ← 2 to k-1 do
4. if (k mod j = 0) then
5. flag_composite ← true;
6. if (flag_composite = false) print k.
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prime.cpp...int main(){ int n(0); bool flag_composite(false);
cout << "Enter n: "; cin >> n;...
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prime.cpp... cout << "Prime numbers:" << endl; for (int k = 2; k <= n; k++) { flag_composite = false; for (int j = 2; j < k; j++) { if (k%j == 0) // if (k mod j == 0) { flag_composite = true; } }
if (!flag_composite) { cout << k << endl; // k is prime } }...
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> prime.exeEnter n: 20235711131719
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for (int k = 2; k <= n; k++) { flag_composite = false; for (int j = 2; j < k; j++) { if (k%j == 0) // if (k mod j == 0) { flag_composite = true; } }
if (!flag_composite) { cout << k << endl; } // k is prime }
Types of Loops
More loopsPretest Loops check the looping condition
first, then begins execution○ while ○ for
Posttest Loops begins execution first, then checks looping condition○ do-while
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Summary while loops:
Repeat until some condition is fulfilled;Pretest loop.
for loops:Used for counting;3 parts: for (initialize; condition; alter){...}
Pretest loop. do-while loops:
Example: “Do you wish to continue?”Posttest loop.
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