Split function in C

#include<stdio.h>
#include<stdlib.h>

int mystrlen(char* val)
{
    int i=0;
    while(val[i]!='\0')
    {
        i++;
    }
    return i++;
}

    char* substring(char* src,int start,int end)
{
    int i,size_src=mystrlen(src);
    if(start>size_src|| start<0)
        return NULL;
    if(end>size_src)
        end=size_src;
    //['a','b','c','d'] 1,3 ['b','c']
    //starts at start and reads up to but not including end,the extra charecter in calloc is to add a '\0' there
    int size_res=end-start;
    char* res=calloc(size_res+1,sizeof(char));
    for(i=0;i<size_res;i++)
    {
        res[i]=src[start+i];
    }
    res[i]='\0';
    return res;
}

    int indexof(char c,char* src)
{
    int i=0;
    int size=mystrlen(src);
    for(i=0;i<size;i++)
    {
        if(c==src[i])
            return i;
    }
    return -1;
}

char* mystrchr(char c,char* src)
{
    int i=0,size=mystrlen(src);
    //must include null charecter
    for(i=0;i<=size;i++)
    {
        if(src[i]==c)
        {
            return src+i;
        }
    }
    return NULL;
}

int count(char c,char* src)
{
    int i,size=mystrlen(src);
    int num=0;
    for(i=0;i<size;i++)
    {
      if(c==src[i])
      {
        num++;
      }
    }
    return num;
}

char** split(char c,char* src)
{
    int i=0,size=mystrlen(src);
    int num=count(c,src);
    int foundAt;
    //For example for the string The0red0ruby0read0to0read,there are five occurences of zero
    //so if you used substring and split you would have ten values,but except for the first and
    //last values,every other value would repeat twice,so remove these from 10...to give you 8/2 non-repeating values
    //the formula: 2+(2n-2)/2 ==>2+n-1 ==>count+1
    num=num+1;

    char** res=calloc(num,sizeof(char*));
    while(i<num)
    {
        foundAt=indexof(c,src);
        if(foundAt==0)
        {
            //ignore...you dont need substring here,instead just increment the pointer to start at the next memory location
            src+=1;
        }
        if(foundAt==-1)
        {
            res[i]=src;
            break;
        }

        if(foundAt>=size)
        {
            //ignore if found at the last charecter or null terminator
            break;
        }
        //you need to use substring here because you need a beginning and an end
        res[i]=substring(src,0,foundAt);
        //pointer arithmetic...
        src=src+foundAt+1;
        if(src==NULL)
        {
            break;
        }
        i++;
    }
    return res;
}

int main(int argc,char** argv)
{
    char* val="The0Red0Riding0Hood0winked0at0the0big0bad0wolf";
    char** res=split('0',val);
    while(*res)
    {
        printf("%s\n",*res);
        res++;
    }
    //free(res);
    return 0;
}