要注意的一點是拼接’\0’,
#include<stdio.h>
#include<string.h>
void vowels(char s1[],char s2[]){
int n=0;
int len=strlen(s1);
for(int i=0;i<len;i++){
if(s1[i]=='a'||s1[i]=='e'||s1[i]=='i'||s1[i]=='o'||s1[i]=='u'){
s2[n]=s1[i];
n++;
}
}
s2[n]='\0';
}
int main(){
char s1[50],s2[50];
scanf("%s",s1);
vowels(s1,s2);
puts(s2);
return 0;
}