题目：
given an array such as
char chars[]={'a',' ','b',' ','c',' ','d'};
write a program that replaces all the blank elements in a character array with the underline character‘_’.
use a pointer,rather than a subscript ,to access the elements of the array.

我自己编的程序：
#include"stdio.h"
main()
{
char chars[]={'a',' ','b',' ','c',' ','d'};
char *p;
int i,t;
p=&chars[1];
for(i=1;i<=3;i++)
{*p='_';
p+=2;}
for(t=0;t<7;t++)
printf("%c",chars[t]);
}

无法输出，请问下下哪里又问题。。，

#include"stdio.h"
main()
{
char chars[]={'a',' ','b',' ','c',' ',' ','d'};
char *p;
int i;
p=&chars[0];
for(i=0;i<8;i++)
{if(*p==' ');
*p='_';
printf("%c",*p);
p=p+1;
}
}


为什么输出时一串---------