Function that counts chars in a string in C

Function that counts chars in a string in C

I am new a C. I would like to get help to finish my function.
The mission is:
Write a function that accepts a string maximum length of 256 characters
containing characters from 'a' to 'z'.
The function to print the number of occurrences of each character.
For example: input abba output will be:
a = 2 b = 2 c = 0 d = 0 .... z = 0
Do not use if during any function.
I would like to get your help to finish this program please.
This is my code
#include "stdlib.h"
#include "conio.h"
#include "stdio.h"
#include "string.h"
#define size 256
void repeat(char *str);
void main()
{
char str[size];
printf("Please enter a string:\n");
flushall;
gets(str);
repeat(str);
system("pause");
return ;
}
void repeat(char *str)
{
char temp=strlen(str);
int i, count=0;
do
{
for (i=0; i<temp ; i++)
{
count += (*str == str[temp-i]);
}
printf("Char %c appears %d times\n ",*str,count);
count=0;
}
while(*(str++));
}