Lecture_02
.pdf1// Fig. 2.7: fig02_07.cpp
2// Class average program with counter-controlled repetition.
3#include <iostream>
4
5 using namespace std;
6
7// function main begins program execution
8int main()
9{
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int total; |
// sum of grades input by user |
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int gradeCounter; |
// number of grade to be entered next |
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int grade; |
// grade value |
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int average; |
// average of grades |
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// initialization |
phase |
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total = 0; |
// initialize total |
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gradeCounter = 1; |
// initialize loop counter |
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// processing phase |
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while ( |
gradeCounter <= 10 ) { |
// loop |
10 times |
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cout << "Enter grade: "; |
// prompt for input |
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cin |
>> grade; |
// |
read grade from user |
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total = total + grade; |
// |
add |
grade to total |
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24gradeCounter = gradeCounter + 1; // increment counter
25}
26 |
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The counter gets incremented |
27 |
// termination phase |
each time the loop executes. |
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average = total / 10; // integer division |
Eventually, the counter causes |
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the loop to end. |
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30// display result
31cout << "Class average is " << average << endl;
33return 0; // indicate program ended successfully Enter grade: 98
34
35 } // end function main Enter grade: 76 Enter grade: 71
Enter grade: 87 Enter grade: 83 Enter grade: 90 Enter grade: 57 Enter grade: 79 Enter grade: 82 Enter grade: 94 Class average is 81
2.10 Assignment Operators
• Assignment expression abbreviations
– Addition assignment operator
c = c + 3; abbreviated to c += 3;
• Statements of the form
variable = variable operator expression;
can be rewritten as
variable operator= expression;
• Other assignment operators
d -= 4 |
(d = d - 4) |
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e *= 5 |
(e = e * 5) |
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f |
/= |
3 |
(f = f |
/ |
3) |
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g |
%= |
9 |
(g = g |
% |
9) |
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2.11 Confusing Equality (==)
and Assignment (=) Operators
• Example
if ( payCode == 4 )
cout << "You get a bonus!" << endl;
–If paycode is 4, bonus given
•If == was replaced with =
if ( payCode = 4 )
cout << "You get a bonus!" << endl;
–Paycode set to 4 (no matter what it was before)
–Statement is true (since 4 is non-zero)
–Bonus given in every case
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2.12 Increment and Decrement
Operators
•Increment operator (++)
–Increment variable by one
–c++
• Same as c += 1 or c = c + 1
•Decrement operator (--) similar
–Decrement variable by one
–c—-
•Same as c -= 1 or c = c - 1
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2.12 Increment and Decrement
Operators
•Preincrement
–Variable changed before used in expression
•Operator before variable (++c or --c)
•Postincrement
–Incremented changed after expression
•Operator after variable (c++, c--)
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2.12 Increment and Decrement
Operators
• If c = 5, then
–cout << ++c;
•c is changed to 6, then printed out
–cout << c++;
•Prints out 5 (cout is executed before the increment.
•c then becomes 6
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2.12 Increment and Decrement
Operators
• When variable not in expression
–Preincrementing and postincrementing have same effect
++c;
cout << c;
and
c++;
cout << c;
are the same
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•1 // Fig. 2.14: fig02_14.cpp
•2 // Preincrementing and postincrementing.
•3 #include <iostream>
•4
•5 using std::cout;
•6 using std::endl;
•7
•8 // function main begins program execution
•9 int main()
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{ |
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int c; |
// declare variable |
•12
•13 // demonstrate postincrement
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c = 5; |
// assign 5 to c |
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cout << c << endl; |
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// print 5 |
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cout << c++ << endl; |
// print 5 then postincrement |
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•17 cout << c << endl << endl; // print 6
•18
•19 // demonstrate preincrement
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c = 5; |
// assign 5 to c |
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cout << c << endl; |
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// print 5 |
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cout << ++c << endl; |
// preincrement then print 6 |
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cout << c << endl; |
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// print 6 |
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return 0; // indicate successful termination |
•26
•27 } // end function main
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