Nested function or calling function in a function

Question

So, I'm not sure how to start, so I'll start with some code:

    int main()
{
    system("cls");
    printf( "1. D4\n" );
    printf( "2. D6\n" );
    printf( "3. D8\n" );
    printf( "4. Exit\n" );
    printf( "Selection: " );
    scanf( "%d", &input );
    switch ( input ) {
        case 1:            
            roll_d4();
            break;

First off, I have this, and when I pick a selection, it works to get me to the function I wanted. So when I get to the D4 function, I have this:

void roll_d4() {
system("cls");
printf("How many D4 do you want to roll?\n");
printf("Enter a number 1-20");
printf("\nSelection: ");
scanf("%d", &input);
switch (input){
    case 5:
    exit(0);
    d4_number();
}

Now, every time I try to run this, it doesn't like the d4_number(); and says it's an implicit declaration. I'm just trying to let you pick a selection and have it go to the next part in the code, in this case a function that will actually roll a die rather than being a menu like this one. But doing it this way isn't working, and I'm at a loss at what to do.

Edit: Code addition. Here's the full program:

#include <stdio.h>
#include <ctype.h>
#include <time.h>
#include <stdlib.h>
#include <stdbool.h>
#include<string.h>
#include<process.h>
#include<conio.h>
#include<ctype.h>
char response;
    int sum = 0;
    time_t t;
    int result;

    int die_d4_1 = 0;
    int die_d4_2 = 0;
    int die_d4_3 = 0;
    int die_d4_4 = 0;
    int die_d4_5 = 0;
    int input;

void roll_d4() {
    system("cls");
    printf("How many D4 do you want to roll?\n");
    printf("Enter a number 1-20");
    printf("\nSelection: ");
    scanf("%d", &input);
    switch (input){
        case 5:
        exit(0);
        d4_number(0);
    }
}
void roll_d6()
{
    printf( "How many D6 do you want to roll?" );
}
void roll_d8()
{
    printf( "How many D8 do you want to roll?" );
}

void d4_number(){
    printf("How many d4 do you want to roll?");
}

int main()
{
    system("cls");
    printf( "1. D4\n" );
    printf( "2. D6\n" );
    printf( "3. D8\n" );
    printf( "4. Exit\n" );
    printf( "Selection: " );
    scanf( "%d", &input );
    switch ( input ) {
        case 1:            /* Note the colon, not a semicolon */
            roll_d4();
            break;
        case 2:          
            roll_d6();
            break;
        case 3:         
            roll_d8();
            break;
        case 4:        
            printf( "Thanks for playing!\n" );
            break;
        default:            
            printf( "Bad input, quitting!\n" );
            break;
    }
    getchar();

}

It's obviously very incomplete, but I'm just trying to solve this problem before adding more.

Answer 1

You need to give d4_number() a prototype, before the call, so the compiler know what arguments it takes and what it returns. Otherwise it still links (for historical reasons) and assumes it returns an int.

Answer 2

If you take a closer look at this code

switch (input){
    case 5:
    exit(0);
    d4_number(0);
}

you can notice that before d4_number function there is an exit function invoked. In that case d4_number function has never a chance to execute because the whole program stops and exits with 0 as a return code.

Other issue is that d4_number function definition does not accept any arguments, but in statement d4_number(0) there is one extra parameter passed.

Answer 3

Okay, I feel like an idiot. All I had to do was move the declaration:

        void d4_number(){
    printf("How many d4 do you want to roll?");
}

above

void roll_d4() {
system("cls");
printf("How many D4 do you want to roll?\n");
printf("Enter a number 1-20");
printf("\nSelection: ");
scanf("%d", &input);
switch (input){
    case 5:
    d4_number(0);
}

so that it was declared before calling...I feel really dumb for this, but thanks everyone for the quick responses!