#include<stdio.h>
void fun(char *p,char *b)
{
int i,k=0;
while(*p)
{
i=1;
while(i<=3 && *p)
{
b[k]=*p;
k++;p++;i++;
}
if(*p)
{
b[k++]=' ';
}
}
b[k]='\0';
}
void main()
{
char a[80],b[80];
printf("Enter a string:");
gets(a);
printf("The original string:");
puts(a);
fun(a,b);
printf("\nThe string after insert space:");
puts(b);
printf("\n\n");
}原文地址:http://blog.csdn.net/u013116579/article/details/38024795