#include <stdio.h>
#include <strings.h>
void fun(char *tab,char *sub){
    int subsize=strlen(sub);
    char num[4];
    char *pch;
    int i=1,numsize;
    pch=strstr(tab,sub);
    while(pch){
        numsize=sprintf(num,"%d",i++);
        memmove(pch+numsize,pch+subsize,strlen(pch+subsize-1));
        memcpy(pch,num,numsize);
        pch=strstr(pch+numsize,sub);
    }
}

int main()
{
    char *tab1 = "Nad rzeczka opodal krzaczka mieszkala kaczka-dziwaczka";
    char *tab2 = "ka";
    fun(tab1,tab2);
    printf("%s",tab1);

    return 0;
}