c function

/*
#include<stdio.h>

int is_prime(int n)
{
    for(int i = 2; i <= n/2; i ++)
        if(n % 2 == 0)
            return 0;
    return 1;
}

int main()
{
    int n;
    
    printf("Enter a number(exit when n<=1):");
    scanf("%d", &n);
    if(is_prime(n) && n > 1)
        printf("%d is a prime number", n);
    else if(n > 1)
        printf("%d is not a prime number", n);
    else
        ;
    
    return 0;
}


#include<stdio.h>

int is_prime(int n)
{
    for(int i = 2; i <= n/2; i ++)
        if(n % 2 == 0)
            return 0;
    return 1;
}
int main()

{
    int n;
    
    printf("Enter a even number(n>=6):");
    scanf("%d", &n);
    if(n < 6 || n%2 != 0)
        printf("error: illegal input
");
    else
        for(int i = 2; i <= n/2; i ++)
            if(is_prime(i) && is_prime(n-i))
                printf("%d = %d + %d
", n, i, n-i);
    return 0;
}



#include<stdio.h>
int fac(int x)
{
    if(x == 1)
        return 1;
    else
        return x*fac(x-1);
}
int main()
{
    int n, m;
    int result;
    
    printf("Enter the value of n and m:");
    scanf("%d %d", &n, &m);
    result = fac(n)/(fac(n-m)*fac(m));
    printf("Result is %d
", result);
    return 0;
}


#include<stdio.h>

void selectMaxAndMin(int A[][4], int row, int c)
//int A[][]: array type has incomplete element type ?
{
    int max, min;
    
    max = min = A[0][0];
    for(int i = 0; i < row; i ++)
        for(int j = 0; j < c; j ++){
            if(A[i][j] > max)
                max = A[i][j];
            if(A[i][j] < min)
                min = A[i][j];
        }
    printf("max = %d, min = %d
", max, min);
}

void main()
{
    int A[4][4] = {1, 5, 3, 6,
                   2, 4, 5, 7,
                   3, 9, 8, 0,
                   4, 1, 9, 5};
    
    selectMaxAndMin(A, 4, 4);
}


#include<stdio.h>

char trans(char c)
{
    if(c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z')
        return c+4;
    else
        return c;
}
void main()
{
    char s[100];
    char c;
    int i;
    
    i = 0;
    while((c = getchar()) != '
')
        s[i++] = trans(c);
    s[i] = '';
    printf("%s
", s);
}

#include<stdio.h>
#define ROW 2
#define COL 3

void trans(int arr[100][100])
//int arr[][100] 无法正常传值？？？？
{
    int k = 0;
    
    printf("transArr:
");
    for(int i = 0; i <= COL; i ++){
        for(int j = 0; j <= ROW; j ++)
            printf("%5d", arr[j][i]);
        printf("
");
    }
} 
void main()
{
    int oriArr[100][100];
    
    printf("Enter the value of oreArr:
");
    for(int i = 0; i <= ROW; i ++)
        for(int j = 0; j <= COL; j ++){
            printf("oriArr[%d][%d]=", i, j);
            scanf("%d", &oriArr[i][j]);
        }
    printf("oriArr:
");
    for(int i = 0; i <= ROW; i ++){
        for(int j = 0; j <= COL; j ++)
            printf("%5d", oriArr[i][j]);
        printf("
");
    }
    trans(oriArr);
}



#include<stdio.h>

char s[100];
void My_char(int i)
{
    if(i == 0)
        printf("%c", s[0]);
    else{
        printf("%c", s[i]);
        My_char(i-1);
    }
}
int main()
{
    char c;
    int i;
    
    i = 0;
    printf("Enter a String:
");
    while((c = getchar()) != '
')
        s[i++] = c;
    printf("After be reverse:
");
    My_char(i-1);

}

*/