为什么变量i在循环中不增加？

Question

What's the problem here? I was trying to concatenate two strings.

Here's the full code. Only first string is printed.

#include<stdio.h>
main()
{
    char s[100],s2[100];
    printf("Enter a String\n");
    scanf("%s",&s);
    printf("Enter second String\n");
    scanf("%s",&s2);
    int i=strlen(s);
    //printf("%d",i);
    int j;


    for(j=0;s2[j]!='\0';++j)
    {
        i+=1;
        s[i]=s2[j];
    }

    printf("%s",s);
}

Answer 1

As already commented, you jump over the terminator of s, change to

for(j=0;s2[j]!='\0';++j)
{
    s[i]=s2[j];
    i+=1;
}
s1[i]='\0'; // terminated after concatenation

and you should be there. Keep in mind that if you dont check the length of the resulting string you may overflow the s[100] array.

Answer 2

If you want write this more secure and dont overflow the s variable use this:

size_t size = strlen(s) + strlen(s2);
char* result = (char*) malloc(sizeof(char) * size + 1);
sprintf(result, "%s%s", size);

This is simple and safe. And do it in function to automatic free s and s2 .