Fundamentals of Programming Session 9 Instructor: Reza - - PowerPoint PPT Presentation
Fundamentals of Programming Session 9 Instructor: Reza Entezari-Maleki Email: entezari@ce.sharif.edu 1 Fall 2013 These slides have been created using Deitels slides Sharif University of Technology Outlines dowhile Repetition Statement
Fall 2013
Sharif University of Technology
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Session 9
These slides have been created using Deitel’s slides
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The do…while repetition statement is similar to the
In
The do…while statement tests the loop-continuation
Therefore, the loop body will be executed at least once. When a do…while terminates, execution continues
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The break and continue statements are used to
The break statement, when executed in a while,
Program execution continues with the next statement. Common uses of the break statement are to escape
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Figure 4.11 demonstrates the break statement in a for
When the if statement detects that x has become 5,
This terminates the for statement, and the program
The loop fully executes only four times.
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In while and do…while statements, the loop-
In the for statement, the increment expression is
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Earlier, we said that the while statement could be used
The
In this case, the increment is not executed before the
Figure 4.12 uses the continue statement in a for
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What is the output of the following code?
int i; for(i=1;i<=10;i++) { if (i==5) continue; printf("%d \n", i); } printf("End\n");
Answer:
1 2 3 4 6 7 8 9 10 End
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What is the output of the following code?
int i; i=1; while (i<=10) { if (i==5) continue; printf("%d \n", i); i++; } printf("\nEnd\n");
Answer:
1 2 3 4
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C provides logical operators that may be used to
The logical operators are && (logical AND), ||
We’ll consider examples of each of these operators. Suppose we wish to ensure that two conditions are
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In this case, we can use the logical operator && as
if if ( gender nder == 1 && a && age >= 65 65 ) ++ ++seniorFem
The table shows all four possible combinations of zero
Such tables are often called truth tables.
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Now let’s consider the || (logical OR) operator. Suppose we wish to ensure at some point in a program
In this case, we use the || operator as in the following
if if ( ( semest mesterAverage age >= >= 90 90 || || finalExa finalExam >= >= 90 90 ) printf printf( ( "St "Student gra grade is A\n" n" ); );
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The && operator has a higher precedence than ||. Both operators associate from left to right. An expression containing && or || operators is evaluated
Thus, evaluation of the condition
gender == 1 && && age age >= >= 65 65
will stop if gender is not equal to 1 (i.e., the entire
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int a=3, b=4, c=4; if (c==3 || b==4 && a==3) printf("%d", (c>=b>=a ? 100 : 200));
200
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C provides ! (logical negation) to enable a programmer to “reverse”
the meaning of a condition.
Unlike operators && and ||, which combine two conditions (and are
therefore binary operators), the logical negation operator has only a single condition as an operand (and is therefore a unary operator).
The logical negation operator is placed before a condition when
we’re interested in choosing a path of execution if the original condition (without the logical negation operator) is false, such as in the following program segment:
if if ( ! ( !( gr grade ade == == se senti ntinel nelValu alue ) ) ) ) prin rintf tf( ( "Th "The e nex next t gra grade de is % s %f\n" n", g , gra rade de ); );
The parentheses around the condition grade == sentinelValue
are needed because the logical negation operator has a higher precedence than the equality operator.
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In most cases, you can avoid using logical negation by
For example, the preceding statement may also be
if if ( grade != ( grade != sentinelValue sentinelValue ) printf printf( ( "The next grade is %f "The next grade is %f\n" n", grade ); , grade );
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There is one type of error that C programmers, no
That error is accidentally swapping the operators ==
What makes these swaps so damaging is the fact that
Rather, statements with these errors ordinarily compile
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For example, suppose we intend to write
if if ( ( payCode payCode == == 4 ) printf printf( ( "You get a bonus!" "You get a bonus!" ); );
if if ( ( payCode payCode = = 4 ) printf printf( ( "You get a bonus!" "You get a bonus!" ); );
The first if statement properly awards a bonus to the
The second if statement—the one with the error—
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The other side of the coin can be equally unpleasant. Suppose you want to assign a value to a variable with a
x = 1;
x == 1;
Here, too, this is not a syntax error. Rather the compiler simply evaluates the conditional
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Figure
Small circles are used in the figure to indicate the single
Connecting individual flowchart symbols arbitrarily can
For simplicity, only single-entry/single-exit control
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Figure 4.18 shows the rules for forming structured programs. Applying the rules of Fig. 4.18 always results in a structured
Notice that Rule 2 generates a stack of control statements; so
Rule 3 is called the nesting rule. Repeatedly applying Rule 3 to the simplest flowchart results
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Rule 4 generates larger, more involved, and more
The flowcharts that emerge from applying the rules in
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