How do I write a simple regular expression pattern matching function in C or C++?

Question

This is a question in my paper test today, the function signature is

int is_match(char* pattern,char* string)

The pattern is limited to only A

Answer 1

A C program to find the index,from where the sub-string in the main string is going to start. enter code here

#include
int mystrstr (const char *,const char *);
int mystrcmp(char *,char *);
int main()
{
    char *s1,*s2;//enter the strings, s1 is main string and s2 is substring.
    printf("Index is %d\n",mystrstr(s1,s2));
    //print the index of the string if string is found
}
//search for the sub-string in the main string
int mystrstr (const char *ps1,const char *ps2) 
{
    int i=0,j=0,c=0,l,m;char *x,*y;
    x=ps1;
    y=ps2;
    while(*ps1++)i++;
    while(*ps2++)j++;
    ps1=x;
    ps2=y;
    char z[j];
    for(l=0;lps4[i])
        return +1;
    else
        return -1;
}