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Hello everyone, I am Ji Ning.
Today is the second day of C language written test training, let's work together!
first question
1. The output of the following program segment is ( )
#include<stdio.h>
int main()
{
char s[] = "\\123456\123456\t";
printf("%d\n", strlen(s));
return 0;
}A : 12 B : 13 C : 16 D : none of the above is correct
So we are going to use vs, let me show you the effect of this code in vs
Haha, there are a few characters that have been clearly distinguished by the compiler. But still, an explanation.
\\: Indicates the character '\', preventing it from being escaped.
\t: Indicates a horizontal tab character, which is the Tab key on the computer, in short it also represents a character.
\ddd: \Add 1~3 numbers, these numbers must be in octal, escaped to a character equivalent to ASCII.
So \\ counts as 1 character, 123456 counts as 6 numeric characters, \123 counts as 1 character, 456 counts as 3 numeric characters, \t counts as 1 character, a total of 12 characters, so choose A.
second question
2. If there is the following program, the output after running is ( )
#include <stdio.h>
#define N 2
#define M N + 1
#define NUM (M + 1) * M / 2
int main()
{
printf("%d\n", NUM);
return 0;
}A : 4 B : 8 C : 9 D : 6
This question examines #define to define macros. The identifiers defined by define are only replaced. If there are no brackets, it may indeed cause some side effects.
Replace the values of N and M into the macro as follows
The value obtained is 8, so choose B.
Knowledge points investigated in this question: C environment and preprocessing
third question
3. The value of f(1) of the following function is ( )
int f(int n)
{
static int i = 1;
if (n >= 5)
return n;
n = n + i;
i++;
return f(n);
}A : 5 B : 6 C : 7 D : 8
This question examines function recursion and static definition of local variables.
When a variable is modified by static, it will not be destroyed after leaving the scope, which means that the value of i enters the function for the first time is 1, and the value of i enters the function for the second time is 2, not every time the value of i is it's 1.
n=1 Enter the function and start recursion
i=1，n=n+i=2
i=2，n=n+i=4
i=3，n=n+i=7
n=7>5 returns n
So choose C for this question .
Function recursion knowledge points: C language function detailed explanation
fourth question
4. Do the following three pieces of program code have the same effect? (
int b;
(1)const int *a = &b;
(2)int const *a = &b;
(3)int *const a = &b;A : (2)=(3) B : (1)=(2) C : Not the same D : All the same
This question examines const modified pointer variables
const modified pointer
When const is on the left of *, the content pointed to by the pointer cannot be changed.
When const is on the right side of *, the pointer variable cannot change its pointing.
In this question, both (1) and (2) const are on the left side of *, belonging to a type, and both restrict the content pointed to by pointer a to be unchangeable; while const in (3) is on the right side of *, belonging to a type, restricting The pointing of the pointer cannot be changed. So choose B for this question .
fifth question
5. Which of the following statements is correct? ( )
A: For struct X{short s;int i;char c;}, sizeof(X) is equal to sizeof(s) + sizeof(i) + sizeof(c)
B: For a double variable a, you can use a == 0.0 to determine whether it is zero
C: The initialization method char a[14] = "Hello, world!"; has the same effect as char a[14]; a = "Hello, world!";
D: None of the above statements are true
This question examines a little more knowledge.
Option A examines the memory alignment content of the structure. If you don’t understand, you can read the structure memory alignment content in the C language custom type , which is written in great detail.
Option B examines floating-point related content. In computer storage, floating-point numbers cannot be stored accurately. To judge whether floating-point numbers are equal, it is generally to judge whether the difference between the two numbers is less than a certain minimum value.
Option C examines concepts related to character pointers and arrays . Its first definition is to store each character of Hello, world into array a; and the second is to assign the address of character 'H' to pointer a, but Hello, world is actually stored in the code in the district.
Statements A, B, and C are all incorrect, so choose D.
Sixth question
6. Nicoches Theorem
Verify the Nicorches theorem, that is: the cube of any integer m can be written as the sum of m consecutive odd numbers.
For example:
1^3=1
2^3=3+5
3^3=7+9+11
4^3=13+15+17+19
Input a positive integer m (m≤100), write the cube of m as the sum of m consecutive odd numbers and output.
Advanced: Time Complexity: O(m), Space Complexity: O(1)
Input description: Input an int integer
Output description: Output the decomposed string
Example:
Input: 6 Output: 31+33+35+37+39+41
This question looks difficult, but it is actually a question of finding the law
Assuming that the cube of m is written as the sum of m consecutive odd numbers, the first output number is:
You only need to output m-1 numbers that add 2 each time and add them together
#include <stdio.h>
int main()
{
int m=0;
scanf("%d",&m);
int i=0;
int sum=0;
for(i=0;i<m;i++)
{
sum+=i;
}
i=sum*2+1;
printf("%d+",i);
m-=2;
while(m--)
{
i+=2;
printf("%d+",i);
}
i+=2;
printf("%d",i);
return 0;
}The difficulty of this question is to correctly control the format of the output.
Seventh question
7, arithmetic progression
Arithmetic sequence 2, 5, 8, 11, 14... (starting from 2, 3 is an arithmetic sequence with a tolerance), output the sum of the first n terms of the arithmetic sequence
Input description: Enter a positive integer n.
Output description: Output an added integer.
Example 1
Input: 2 Output: 7
Example 2
Input: 275 Output: 113575
This question is relatively simple, just give the code to everyone.
#include <stdio.h>
int main()
{
int n=0;
scanf("%d",&n);
int i=0;
int ret=2;
int sum=0;
for(i=0;i<n;i++)
{
sum+=ret;
ret+=3;
}
printf("%d",sum);
}