Linux system function call experiment

Linux system function call experiment

The purpose of the experiment: to
understand the use of system functions of the Linux operating system

Experimental content:
Create a test user, the password is also test.
After logging in with test, create the src directory, and all source code, intermediate code, and target code are placed in the / home / test / src directory.

1. Write a simple c language program: the function int input (int a [], int n) is used to input an integer array with n elements, and void output (int b [], int n) is used to output n elements Integer array, the function int sum (int a [], int n) is used for array summation, and the function input, output, sum are called in turn in the main function.

#include<stdio.h> 
#define N 100
int input(int a[],int n)
{
 int i;
 for(i=0;i<n;i++)
 {
  scanf("%d",&a[i]);
 }
 return 0;
}
void output(int b[],int n)
{
 int i;
 for(i=0;i<n;i++)
 {
  printf("%2d",b[i]);
 }
}
int sum(int a[],int n)
{
 int sum=0;
    int i;
    for(i=0;i<n;i++)
    {
     sum=sum+a[i];
 }
 printf("%d",sum);
 return sum;
}
int main()
{
 int n,a[N];
 printf("input n：");
 scanf("%d",&n);
 printf("input number：");
 input(a,n);
 printf("output：");
 output(a,n);
 printf("\n");
 printf("sum：");
 sum(a,n);
 printf("\n");
 return 0;
}

2. Write a simple c language program: use the random number function to generate two integer numbers, and perform arithmetic operations based on the input characters '+', '-', '*', and '/' (Addition, subtraction, multiplication and division of symbols and numerical expressions, how should be parsed and calculated).

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int main()
{
 int i,a,b;
 int m,n,p;
 float q;
 char c;
 srand((int)time(0));
 for(i=0;i<2;i++)
 {
  a=1+(int)(4.0*rand()/(RAND_MAX+1.0));
  b=1+(int)(4.0*rand()/(RAND_MAX+1.0));
 }
 printf("%d %d\n",a,b);
 printf("Please input:+、-、*、/\n");
 c=getchar();
 m=a+b;
 n=a-b;
 p=a*b;
 q=(float)(a/b);
 switch(c)
 {
  case'+':printf("sum:%d\n",m);
  break;
  case'-':printf("difference:%d\n",n);
  break;
  case'*':printf("product:%d\n",p);
  break;
  case'/':printf("shang:%d\n",q);
  break;
  default:
  printf("error!");
 }
 return 0;
}

#include<stdio.h>
#include<stdlib.h>
#include<ctype.h> 
#define N 10000 
static int compare (const void  *a, const void  *b)
{
   return ( *(int*)a - *(int*)b );
}
int main()
{
 int a[N];
 int n;//array length 
 int i;
 printf("please input n:\n");
 scanf("%d",&n);
 printf("please input a[]:");
 for( i=0;i<n;i++)
 {
  scanf("%d",&a[i]);
 }
 qsort(a,n,sizeof(a[0]),compare);
 for( i=0;i<n;i++)
 {
  printf("%d",a[i]);
 }
 printf("\n");
 int key;
 printf("please input the key:");
 scanf("%d",&key);
 int *item=NULL;
 item=bsearch(&key,a,n,sizeof(a[0]),compare);
 if(item == NULL)
  printf("%d is not in the array\n",key);
 else
  printf("%d is  in the array\n",key,*item);
 return 0;
}