Question

I’m trying to write a functions to modify strings in C.
If I have a function like

char *func(char *s){
    char *t=s;
    s++;     //option 1
    t++;     //option 2
    *t='a';  //option 2
    return s;
}

If I do something like [option 1]: s++; I believe it will return the pointer to wherever s is now pointing. If I do [option 2]: t++; and *t='a'; then return s, will it return the address for the first spot of s but with modified contents or will it return the address with the original content?

Answer 1

If I do t++; and *t=’a’; then return s, will it return the address for
the first spot of s but with modified contents or will it return the
address with the original content?

I believe your question assumes something like this:

char s[] = "abcde";
char *t = s;
t++;
*t = 'a';

Here you’ve got one string and two pointers that initially both point to the beginning of the string. At the third line, you modify one of the pointers to point to the next character. At the fourth line, you modify the data at that location. Since s points to the same data, and the data is modified, the string that s points to will change.

printf("s is: %s\n", s");   // s is: aacde
printf("t is: %s\n", t");   // t is: acde

BTW, there’s no better way to really learn this stuff than to write little test programs and play with them. A good book will explain how things are supposed to work, but playing with code is the way that you grow to really understand the code and believe what the books tell you.