Little knowledge about C language (array and string)

（1）memset(a,0,sizeof(a)) The function of is to put the array a Zero clearing , It's also in string.h In the definition of . Use memset Than for Circulation is more convenient 、 quick .

#include <stdio.h>
#include<string.h>
int main () {
  int a[5];
  memset(a,0,sizeof(a));
	return 0;
}

（2） If from array a Copied to the k Elements to arrays b, You can use this statement ：memcpy(b,a,sizeof(int)*k).

Use memcpy The function contains the header file string.h. If you need to put the array a Copy all to the array b in , It can be written. ：memcpy(b,a,sizeof(a)).

#include <stdio.h>
#include<string.h>
int main () {
  int a[]={1,2,3,4,5};
  int b[5];
  memcpy(b,a,sizeof(a));
	return 0;
}

（3） stay stdlib.h There's a function in atoi, Its function prototype is as follows ：int atoi(char *s)

It means that the string s Convert the contents of into an integer number and return , Such as a string “1234”, Then the return value of the function is 1234.

#include <stdio.h>
#include<stdlib.h>
int main () {
  printf("%d",atoi("1234"));
  return 0;
}

（4） stay stdlib.h There's a function in itoa, It means that the integer value Convert to a string and store it in string.

for example ,itoa(32,string,10) Yes, it will 32 Become a string of decimal numbers “32”, And return a pointer to this string ;

#include <stdio.h>
#include<stdlib.h>
#include<string.h>
int main () {
  char a[10];
  printf("%s",itoa(32,a,10));
	return 0;
}

（5）sprintf It's a variable parameter function , The function of this function is to write the formatted data into a string , Its return value is string length . The header file containing this function is stdio.h.

for example , The function of this program is to convert integers 123 Print as string and store in character array a[ ] in .

#include <stdio.h>
int main () {
  char a[10];
  int len=sprintf(a,"%d",123);
  printf("%d",len);
	return 0;
}

（6）strchr The function of finding string is s First character in c The location of . Its return value is the first occurrence of the return c A pointer to the position of , If s Does not exist in the c Then return to NULL. The header file containing this function is string.h.

#include <stdio.h>
#include<string.h>
int main () {
  char a[]={"hello word"};
  char b='h';
  char *c=strchr(a,b);
  printf("%c",*c);
	return 0;
}