To define an array ： A set of several variables with a certain order relationship , The data type of variables must be the same

Array classification ：1. Array of values , A character array , Pointer array , Array of structs .

One dimensional array

1. An array with only one subscript ：< data type >< Array name >【< Constant expression >】

2. The array name should conform to the naming rules of identifiers

3. The array name cannot be the same as other variables

4. Constants in square brackets indicate the number of array elements

5. The array name represents the first address of memory , Is the address constant

6. Allocate continuous memory to the array at compile time .

A reference to a one-dimensional array

1. Arrays must be referenced element by element , Instead of quoting as a whole

2. Pay attention to subscripts from 0 Start , The scope is 0-n-1.

One dimensional array initialization

1. For ordinary local arrays, do not initialize , The value of the element in the array is uncertain .

2. about static Decorated array , Not initialized , The element defaults to 0.

3. The global array is not initialized , The array element defaults to 0;

4. All initialization ,int a[]={1,2,3,4,5}; Note that it can only be written in one line, not newline .

5. Partial initialization , Other automatic assignment 0;

6. The elements of an array cannot be assigned as a whole , Only a single assignment can be made .

Multidimensional arrays

1. Definition ： Have two or more subscripts , It's called multidimensional arrays example ：a[10][10]

2.< data type >< Array name >[ Constant expression 1][ Constant expression 2]

Constant expression 1 Is the number of rows , expression 2 Is the number of columns , The number of rows can be omitted , But the second dimension column number cannot be omitted .

3. initialization ：

Initialize by line , The initial value of each line is {} Cover up int a[2][3]={ {1,2,3},{4,5,6}};

Initialize in element order int a[2][3]={1,2,3,4,5,6};

4. Memory allocation ： It's like a one-dimensional array , Priority by line , Memory is still continuous .

Character arrays and strings

1. Definition ： Character array is an array whose element data type is character type .char c[] char c[][10];

2. initialization

Assign values character by character

Use string constants to assign values , Note that the end of the string has \0, So the actual memory needs to occupy an extra byte , Pay attention to the problem of cross-border .

3. Definition of string ： Referring to ‘\0’ A group of characters as closing characters , When storing a string into an array , Also put the special Terminator '\0' Deposit in , As the end of this string .

4. Input and output of string

printf("%s") When outputting the contents of the character array, it will be output until '\0' character

scanf("%s") When the input , End in case of blank space or carriage return .

String handling functions

1. String copy function strcpy /strncpy

Format ：strcpy( A character array 1, A character array 2)  / strncpy( A character array 1, A character array 2,number)

function ： The string 2 Copy to character array 1 in / Put the character array 2 Before n Copy to character array 1

Return value ： Returns an array of characters 1 The first address

Be careful ： A character array 1 It has to be big enough , Copy even '\0' Copy together

2. String concatenation function strcat / strncat

Format ：strcat( A character array 1, A character array 2)/strnact( A character array 1, A character array 2,number)

function ： Put the character array 2 Connect to character array 1 after / Put the character array 2 front n Connect to character array 1

Return value ： A character array 1 The first address

Be careful ： A character array 1 Big enough , Array 1 Of \0 Delete , Add \0

3. String comparison function strcmp / strncmp

Format ：strcmp( character string 1, character string 2)/strncmp( character string 1, character string 2,number)

function ： Compare strings from left to right 1 And string 2（ASCII value ） size , Until you encounter different characters / Compare the front from left to right n Character size

Return value ：= Return to 0  < Returns a negative number > Return as a positive integer

4. String length function strlen

Format strlen( Character array name )

function ： Calculate the effective length of the string

Return value ： Returns the actual length of the string , barring \0

When you translate \ Not included \xhh Express 16 Hexadecimal number ,\ddd Represents octal number

Practical example

1.#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[])
{ 
    char ch1[100]="hello";
    char ch2[]="hewlo";
    char ch3[]="\x69\144\n";
    int a,b;
    strcat(ch1,ch2);// String concatenation function
    puts(ch1);
    putchar('\n');
    //strcpy(ch1,ch2);// String copy function
    //puts(ch1);
   // putchar('\n');
    a=strcmp(ch1,ch2);// String comparison function
    printf("%d\n",a);
    b= strlen(ch3);// String effective length function
    printf("%d\n",b);
    return 0;
} 

2.#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[])
{ 
    char arr1[100]={};
    char arr2[]="hello brother";
    strncpy(arr1,arr2,5);
    puts(arr1);
    putchar('\n');
    return 0;
} 

3.

// Calculate the top ten items of Fibonacci series and output the results in reverse order
// Fibonacci sequence , The latter element is the sum of the first two elements
#include <stdio.h>

int main(int argc, char *argv[])
{ 
    int disc[10];
    disc[0]=disc[1]=1;
    int i;
    for(i=2;i<10;i++)
    {
        disc[i]=disc[i-1]+disc[i-2];
    }
    for(i=9;i>=0;i--)
    {
        printf("%d ",disc[i]);
    }
    return 0;
} 

4. bubble sort
#include <stdio.h>
#define N 10
int main(int argc, char *argv[])
{   
    int i,j,t;
    int a[N];
    printf("please input %d numbers\n",N);
    for(i=0;i<N;i++)// Loop input elements
        scanf("%d",&a[i]);
    for(i=0;i<N-1;i++)// The first level of the cycle is a cyclic sort N-1 Time
        for(j=0;j<N-1-i;j++)// The second cycle , Compare sizes and swap elements , Every time you compare, the number of cycles will be reduced by one
        {
            if(a[j]>a[j+1])// If the current element is larger than the next one, exchange elements
            {
                t=a[j];
                a[j]=a[j+1];
                a[j+1]=t;
            }
        }
    for(i=0;i<N;i++)// Loop out array elements
        printf("%5d",a[i]);
    printf("\n");
    return 0;
} 

5. Choose the sorting method

#include <stdio.h>
#define N 10

int main(int argc, char *argv[])
{ 
    int a[N],i,j,r,t;
    printf("please input %d numbers\n",N);
    for(i=0;i<N;i++)
        scanf("%d",&a[i]);
    for(i=0;i<N-1;i++)// Through N-2 Second comparison
    {
        r=i;
        for(j=i+1;j<N;j++)// If the latter is smaller than the former , Will R and J Exchange , Then cycle and compare with the next bit
        {
            if(a[j]<a[r])
                r=j;
        }
        if(r!=i)// If R Not equal to I It means that the smallest one is the current number R position , Then connect him with I Bit exchange
        {
            t=a[r];
            a[r]=a[i];
            a[i]=t;
        }

    }
    printf(" From childhood, the output is ：\n");
    for(i=0;i<N;i++)
        printf("%5d",a[i]);// Cyclic output
    printf("\n");
    return 0;
}

6. Print the first ten lines of Yang Hui triangle
#include <stdio.h>

int main(int argc, char *argv[])
{ 
    int a[10][10]={ {0}};
    int i,j;
    for(i=0;i<10;i++)
    { 
        a[i][0]=1;// Cycle to assign all the first column 1
        for(j=1;j<=i;j++)// Control the number printed as triangle
            a[i][j]=a[i-1][j-1]+a[i-1][j];// Find the rule and get the expression
    }
    for(i=0;i<10;i++)
    {
        for(j=0;j<=i;j++)
            printf("%-8d",a[i][j]);//- Will make the number followed by a space
        printf("\n");
    }
    return 0;

} 

7. Enter a string , Then output it in reverse order
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[])
{ 
   /* char arr[100]={0};// If not initialized , Random values will be assigned later , Result in output garbled code
    int i,n;
    printf("please input word\n");
    gets(arr);
    n=sizeof(arr)/sizeof(char);
   // n=strlen(arr);
    for(i=n-1;i>=0;i--)// Change the output order to achieve reverse output
        putchar(arr[i]);
    putchar('\n');
    return 0;*/
    char arr[100]={0},ch;// Exchange positions to achieve reverse order output
    int i,j,n;
    printf("please input a string:");
    gets(arr);
    i=0;
    n=strlen(arr);
    j=n-1;
    while(i<j)
    {
        ch=arr[i];
        arr[i]=arr[j];
        arr[j]=ch;
        i++;
        j--;
    }
    puts(arr);
    return 0;
} 

8. Change the uppercase in the input string to lowercase , Lowercase to uppercase
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[])
{ 
    char arr[10]={0};
    int n,i;
    fgets(arr,sizeof(arr),stdin);// There is enough space to save the Enter key
    n=strlen(arr);
    for(i=0;i<n;i++)
    {
        if(arr[i]>='A'&&arr[i]<='Z')
            arr[i]=arr[i]+32;
        else if(arr[i]>='a'&&arr[i]<='z')
            arr[i]=arr[i]-32;
    }
    puts(arr);
    return 0;
} 

9. Find the maximum number in the array
#include <stdio.h>

int main(int argc, char *argv[])
{ 
    int max,i;
    int a[10]={0};
    printf("please input 10 number\n");
    for(i=0;i<10;i++)
    {
        scanf("%d",&a[i]);
    }
    max=a[0]; 
    for(i=1;i<10;i++)
    {
        if(a[i]>max)
        {
            max=a[i];   
        }
    }
    printf("max=%d\n",max);
    return 0;
} 

10. Input 10 An integer is stored in a one-dimensional array , Statistics output the positive number , The number of negative numbers and zeros
#include <stdio.h>
int main(int argc, char *argv[])
{ 
    int a[10],i;
    int j=0;
    int k=0;
    int m=0;
    printf("please input 10 number\n");
    for(i=0;i<10;i++)
        scanf("%d",&a[i]);
    for(i=0;i<10;i++)
    {
        if(a[i]==0)
        {
            j++;
        }
        else if(a[i]>0)
        {
            k++;
        }
        else 
        { 
            m++;

        }
    }
    printf(" A positive number is %d\n The number of negative numbers is %d\n The number of zeros is %d\n",k,m,j);
    return 0;
} 

11. Input 10 An integer is stored in a one-dimensional array , Then store in reverse order and output
#include <stdio.h>
int main(int argc, char *argv[])
{ 
    int a[10],i,t;
    printf("please input 10 number\n");
    for(i=0;i<10;i++)
        scanf("%d",&a[i]);
    for(i=0;i<5;i++)
    {
        t=a[i];
        a[i]=a[9-i];
        a[9-i]=t;
    }
    for(i=0;i<10;i++)
        printf("%d ",a[i]);
    return 0;
}