how do i define a function in C that writes an int or a char from a given string pointer
To create a function in C that writes an int or a char from a given string pointer, you need to determine how to distinguish between an int and a char within the string. In this example, let's assume that you have a string that contains only digits and letters (no spaces or other characters). We'll create a function that takes a pointer to a string and an index, and prints the int or char at the specified index.

Here's a simple example:
``` 
#include <stdio.h>
#include <ctype.h>

void print_int_or_char(const char* str, int index) {
    char c = str[index];
    
    if (isdigit(c)) {
        int num = c - '0'; // Convert the char digit to an integer value
        printf("Integer: %d\n", num);
    } else if (isalpha(c)) {
        printf("Character: %c\n", c);
    } else {
        printf("Invalid input\n");
    }
}

int main() {
    const char* input_string = "a1b2c3";
    int index = 2; // Specify the index of the character you want to print
    
    print_int_or_char(input_string, index);

    return 0;
}
``` 
In this example, the print_int_or_char function takes a string pointer and an index as its arguments. The function checks if the character at the specified index is a digit or a letter. If it's a digit, it converts the character to an integer value and prints it. If it's a letter, it prints the character directly. If the input is neither a digit nor a letter, the function prints an "Invalid input" message.