How to make a char equal to user input?

Question

For example if the char was 4 blank spaces

_ _ _ _
_ _ _ _

Then the user enters 1234, I want it to look like

1 2 3 4 
_ _ _ _

I have tried things like

grid[1][1] = let1; // let1 is the variable of the first number the user inputs, it's an int

but it's not working. Do you have any ideas on how I can do this?

Answer 1

Edited Original content of question has changed significantly since first posting this. Therefore a disclaimer:

This answer applies to the Title question and original content of question plus the section in the first `else if` statement to address latest OP edit.

One way can use command line arguments (requires using C signature int main(int argc, char *argv[]);) and then enter the digits 1 2 3 4 with space just as you have illustrated, then convert them in the following ways using format specifiers and in one case using a string to number conversion function:

Compile the following code into an exe.

int main(int argc, char *argv[])
{
    
    if(argc == 1)
    {
        printf("%c %c %c %c\n", '_','_','_','_');
        printf("%c %c %c %c\n", '_','_','_','_');
    }
    else if(argc == 2 && strlen(argv[1]) == 4)
    {
        //if entering 1234 and need output 1 2 3 4
        printf("%c %c %c %c\n", argv[1][0], argv[1][1], argv[1][2], argv[1][3]);
        printf("%c %c %c %c\n", '_','_','_','_');
        
    }
    else if(argc == 5)
    {
        //three options: char, string, number
        printf("%c %c %c %c\n", argv[1][0], argv[2][0], argv[3][0], argv[4][0]);//print char
        printf("%c %c %c %c\n", '_','_','_','_');
        printf("%s %s %s %s\n", argv[1], argv[2], argv[3], argv[4]);//print pointer to char (string)
        printf("%c %c %c %c\n", '_','_','_','_');
        printf("%d %d %d %d\n", atoi(argv[1]), atoi(argv[2]), atoi(argv[3]), atoi(argv[4]));//print integer
        printf("%c %c %c %c\n", '_','_','_','_');
        
        
    }
    else printf("Wrong number of inputs.  Try again\n");
    
    getchar();
    
    return 0;
}

On command line enter

program.exe 1 2 3 4  //using the real name of your program