[C]atoiの使い方

#include <stdio.h>
#include <stdlib.h>

int main(){
int num = 0;
char myString[20] = "2019";

printf("string = %s\n",myString);
//2019 출력
num = atoi(myString);
printf("int = %d\n",num);
//2019 출력

char str1[]="testing";
char str2[]="2019";
char str3[]="2021testing";
char str4[]="testing2022";

printf("int = %d\n",atoi(str1));
//0
printf("int = %d\n",atoi(str2));
//2019
printf("int = %d\n",atoi(str3));
//2021
printf("int = %d\n",atoi(str4));
//0
}