- ECE206 Programming
Lecture 5 Control Structure (II)
09/06/07
Recap
Sequence structure Selection structure
if/ifelse/ifelse if ladder/nested ifs Conditional expressions Switchcase/controlling expression Dangling else problem
Repetition structure
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1
Why repetition?
int number1, number2, number3; float avg;
No Calculate sum
cout << Please input 3 integer numbers:\n cin >> number1 >> number2 >> number3; avg = (number1+nubmer2+number3)/3.0; cout << The average is << avg << endl;
1000th number? Yes Calculate avg.
What about 1000 numbers?
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Key components in repetition
Where to start and when to stop
Counter-controlled Sentinel-controlled Task-controlled
Controlling expression What action to perform How to jump out from repetition
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2
for loop
1 2 3 4
for (initialization; expression; increment) { statement sequence; }
Initialization expression true? True Statement sequence increment
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False
Example 1 for
for (i=10; i>=-10; i=i-5) { cout << i << ; } for (i=0; i<5; i++) { cout << i << ; } for (i=0; i!=10; i++) { cout << i << ; } for (char i=A; i<F; ++i) { cout << i << ; }
Calculate the sum of all even numbers less than 1000.
C++: int total = 0; for ( int even=2; even<1000; even=even+2 ) total += even;
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3
Exploring - for loop
The infinite loop
for ( ; ; ) { // }
How to stop infinite loop?
Time delay loops
for (x=0; x<1000; x++); for (x=0; x<1000; x++) for (y=0; y<1000; y++);
;?
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while loop
initialization while (condition) { statements; } expression true? False True statements
;?
Find the smallest power of 2 greater than 1000. C++: int product = 1; while ( product <= 1000 ) product = 2 * product;
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4
Example 2 while
/* This program displays all printable characters. * * Notes: ch Since is an unsigned character, it can only hold * the values from 0 to 255. When it holds the value 255 and is then * incremented, its value will "wrap around" to zero. */ #include <iostream> using namespace std; //introduces namespace std int main( void ) { unsigned char ch; ch = 32; while (ch) { cout << (char)ch; ch++; } return 0; }
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do while loop
;? do { statements; } while (expression);
statements expression true? False True
Find the smallest power of 2 greater than 1000.
C++: int product = 1; do { product = 2 * product; }while ( product <= 1000 );
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5
Examples 3 - while and do..while
x = 10; while (x > 0) { x--; cout << x; } x = 10; do { x--; cout << x; } while (x>0);
The difference lies in the order of execution: in do..while, the statement is executed first, then the condition; in while, the condition is executed first, then the statement if condition is satisfied
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Example 4 the jump structure
continue: to force an early iteration of a loop to bypass the loops normal control structure break: to force an immediate exit from ...