C language must memorize 18 classic programs that beginners of C language must know (collection)

AC languageHow do beginners learn code, read code and write code? I want to learn code but don’t know the direction. Who can give me a direction? For In C language, there are not many things to remember, it is basically just a few common statements plus some keywords. The thousands or even tens of thousands of lines of code you see are all written repeatedly using these statements and keywords. It's just that their logical functions are different. So how to quickly get started with C language code? It is recommended to read more and write more.

1. The first of 18 classic programs that must be memorized in C language is the multiplication table.

Use C language to output the 9*9 formula. There are 9 rows and 9 columns in total, i controls the rows and j controls the columns.

2. C language must memorize 18 classic programs for 4×4 array

The function of the following program is to convert a 4 The ×4 array is rotated 90 degrees counterclockwise and then output. The data of the original array is required to be randomly input. The new array is output in the form of 4 rows and 4 columns. Please complete the program in the blank space.

3. C language must memorize 18 classical problems related to classic programs

There is a pair of rabbits, the third one from birth A pair of rabbits are born every month starting from 3 months old, and another pair of rabbits are born every month after the rabbit reaches the third month. If the rabbits do not die, what is the total number of rabbits each month?

The pattern of rabbits is the sequence 1,1,2,3,5,8,13,21...

4. C language must Memorize 18 classic programs for prime numbers

Determine how many prime numbers there are between 101-200, and output all prime numbers and the number of prime numbers.

Program analysis: How to determine prime numbers: Use a number to divide 2 to sqrt (this number) respectively. If it can be divided evenly, it means that the number is not a prime number, otherwise it is a prime number.

5. C language must memorize the complete number-related codes of 18 classic programs

If a number is exactly equal to its factor The sum is called a "perfect number". For example, 6=1+2+3. Program to find all perfect numbers within 1000.

6. C language must memorize 18 classic programs for triangle printing

Programming to print right-angled Yang Hui triangle

7. Question about the average score of 18 classic programs that must be memorized in C language

Enter the scores of 3 students in 4 courses through the keyboard, and find out respectively Average grade per student and average grade per course. All scores are required to be put into an array with 4 rows and 5 columns. When inputting, use spaces between data for the same person and press Enter for different people. The last column and the last row contain the average score of each student and the average score of each course respectively. and overall class average.

#include <stdio.h>
#include <stdlib.h>
main()
{ float a[4][5],sum1,sum2;
  int i,j;
  for(i=0;i<3;i++)
    for(j=0;j<4;j++)
      scanf("%f",&a[i][j]);
  for(i=0;i<3;i++)
  { sum1=0;
    for(j=0;j<4;j++)
      sum1+=a[i][j];
      a[i][4]=sum1/4;
  }
  for(j=0;j<5;j++)
  {  sum2=0;
     for(i=0;i<3;i++)
       sum2+=a[i][j];
       a[3][j]=sum2/3;
   }
   for(i=0;i<4;i++)
   {  for(j=0;j<5;j++)
      printf("%6.2f",a[i][j]);
      printf("\n");
   }
}

8. C language must memorize the reverse output of 18 classic programs

Improve the program to output the input string in reverse order, such as inputting windows output swodniw.

9. The ninth C language must memorize 18 classic programs

The function of the following program is to select from the character array s Delete the characters stored in c.

10. You must memorize 18 classic programs in C language----solve sorting problems

Write a void sort(int *x, int n) implements sorting the n data in the x array from large to small. n and array elements are input in the main function. Display the result on the screen and output it to the file p9_1.out

 #include<stdio.h>
void sort(int *x,int n)
{
int i,j,k,t;
for(i=0;i<n-1;i++)
{
 k=i;
 for(j=i+1;j<n;j++)
   if(x[j]>x[k]) k=j;
   if(k!=i)
   {
    t=x[i];
    x[i]=x[k];
    x[k]=t;
   }
}
}
void main()
{FILE *fp;
     int *p,i,a[10];
     fp=fopen("p9_1.out","w");
    p=a;
printf("Input 10 numbers:");
for(i=0;i<10;i++)
  scanf("%d",p++);
p=a;
sort(p,10);
for(;p<a+10;p++)
 {  printf("%d ",*p);
        fprintf(fp,"%d ",*p);  }
        system("pause");
    fclose(fp);
}

11. C language must memorize 18 classic programs to solve the problem of sorting from small to large

Known The elements in array a have been arranged in order from small to large. The function of the following program is to insert an input number into array a. After the insertion, the elements in array a are still arranged in order from small to large

12、C语言必背18个经典程序之替换输出

编写函数replace(char *s,char c1,char c2)实现将s所指向的字符串中所有字符c1用c2替换，字符串、字符c1和c2均在主函数中输入，将原始字符串和替换后的字符串显示在屏幕上，并输出到文件p10_2.out中

#include<stdio.h>
replace(char *s,char c1,char c2)
{ while(*s!='\0')
   {  if (*s==c1)
         *s=c2;
         s++;
   }
}
main()
{ FILE *fp;
  char str[100],a,b;
   if((fp=fopen("p10_2.out","w"))==NULL)
      { printf("cannot open the file\n");
       exit(0);                     }
   printf("Enter a string:\n");
    gets(str);
    printf("Enter a&&b:\n");
    scanf("%c,%c",&a,&b);
printf("%s\n",str);
fprintf(fp,"%s\n",str);
replace(str,a,b);
printf("The new string is----%s\n",str);
fprintf(fp,"The new string is----%s\n",str);
fclose(fp);
}</stdio.h>

13、C语言必背18个经典程序之查找

在一个字串s1中查找一子串s2，若存在则返回子串在主串中的起始位置，不存在则返回-1。 

14、C语言必背18个经典程序，用指针变量输出结构体数组元素。

struct student
{
 int num;
 char *name;
char sex;
int age;
}stu[5]={{1001,"lihua",'F',18},{1002,"liuxing",'M',19},{1003,"huangke",'F',19},{1004,"fengshou",'F',19},{1005,"Wangming",'M',18}};
main()
{int i;
struct student *ps;
printf("Num \tName\t\t\tSex\tAge\t\n");
/*用指针变量输出结构体数组元素。*/
for(ps=stu;ps<stu+5;ps++)
printf("%d\t%-10s\t\t%c\t%d\t\n",ps->num,ps->name,ps->sex,ps->age);
/*用数组下标法输出结构体数组元素学号和年龄。*/
for(i=0;i<5;i++)
printf("%d\t%d\t\n",stu[i].num,stu[i].age);
}

15、C语言必背18个经典程序之十五

建立一个有三个结点的简单链表

16、C语言必背18个经典程序之冒泡排序

冒泡排序，从小到大，排序后结果输出到屏幕及文件myf2.out 

17、输出字符串的C语言必背经典程序

输入一个字符串，判断其是否为回文。回文字符串是指从左到右读和从右到左读完全相同的字符串。

18、C语言必背18个经典程序之编写函数

编写函数countpi，利用公式计算π的近似值，当某一项的值小于10-5时，认为达到精度要求，请完善函数。将结果显示在屏幕上并输出到文件p7_3.out中。

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