Basic questions about C Language

1. If int A = 1, B = 2, c = 3, D = 4; then the conditional expression "A <B? A: C <D? The value of C: D is __?

Resolution: Condition operator? : The combination is from right to left, then the combination of the expression is represented in parentheses: (A <B? A: (C <D? C: d ))
Answer: 1

2. I = 10 is known; the value of the expression "20-0 <= I <= 9" is __?

Analysis: in binary operators, Arithmetic Operators have the highest level, Relational operators followed by logical operators. The concatenation of expressions is represented by parentheses (20-0) <= I <= 9
Answer: 1

3. Int x = 1; U is known. Run the statement "Y = ++ x> 5 & ++ x <10;" and the value of variable X is __?

Resolution: In an expression, the single object operator ++ is the highest, the relational operator level is higher than the logical operator level, and the value assignment operator = is the lowest. The concatenation of expressions is represented by brackets y = (++ X)> 5) & (++ X) <10). For logical operators &&, when the preceding part is false, the latter part is not calculated. Therefore, the result (++ X)> 5) is false, followed by (++ X) <10) so the result of X is 2, and the result of Y is 0.
Answer: 2

4. Int I = 1 is known; execute the statement "while (I ++ <4);" and the variable I value is __?

Resolution: N ++ indicates that the value of Variable N is used first, and then the value of N is increased by 1; + + N indicates that the value of N is increased by 1, and then the value of Variable N is used. For example, if the * PTR ++ and * (PTR ++) results are consistent, they all indicate "First * PTR, then PTR ++ ".
Answer: 5

5. macro definition:
# Define PR (FMT, Val) printf (# Val "= %" # FMT "/T", (VAL ))
# Define NL putchar ('/N ')
# Define print1 (F, X1) Pr (F, X1), NL
So, print1 (d, 5); what are the extended results?

// This call is first extended to RP (d, 5) nL
// Then extend printf (#5 "= %" # D "/T", (5), putchar ('/N ')
// Last extended printf ("5 = % d/T", (5), putchar ('/N '))
From C language confusing

 

6. programming style selection of correct conditions

(1)
Do
{
If (! A) continue;
Else B;
C;
} While ();

// For the first transformation, remove the "redundant" Continue statement first.
Do {
If (a) {B; C ;}
} While ();

// For the second transformation, replace the "Do... while" and if statements with the while statements.
While ()
{
B; C;
}

 

(2)

While (C = getchar ()! = '/N ')
{
If (C = '') continue;
If (C = '/t') continue;
If (C <'0') Return (other );
If (C <= '9') Return (DIGIT );
If (C <'A') Return (other );
If (C <= 'Z') Return (alpha );

Return (other );
}
Return (EoL );

 

After Transformation:

While (C = getchar ()! = '/N ')
{
If (C> = 'A' & C <= 'Z') return Alpha;
Else if (C> = '0' & C <= '9') return digit;
Else if (C! = ''& C <= '/t') return Other;
}
Return (EoL );

From C language confusing

 

7. A question about pointers
Int P;
* P ++ = * (p ++)
* ++ P = * (++ P)
+ + * P = ++ (* P)

 

8.
Int A [3] [3] = {1, 2, 3}, {4, 5, 6}, {7, 8, 9 }};

The values of a and a [0] are the same address, but they are different. Their types are different, which results in the same expression in the arithmetic operation on the address, A + 1 and a [0] + 1 have different meanings. The former points to the next ternary int array, and the latter points to the next int integer pointer.