Dev - C++ - Como puedo hacer que funcione

#include <stdio.h>

int PedirDato(){

int n;

printf ("Escribe un numero: ");

scanf ("%i", &n);

return (n);

}

int suma (int n1){

int r;

r=r+n1;

return (r);

}

int resta (int n1){

int r;

r=r-n1;

return (r);

}

int multiplicacion (int n1){

int r;

r=r*n1;

return (r);

}

int division (int n1){

int r;

r=r/n1;

return (r);

}

int main (){

int n1,Op,i;

while (Op!=5){

printf (" \n 1:suma, \n 2:resta, \n 3:multiplicacion, \n 4:division, \n 5:salir");

scanf ("%i", &Op);

switch (Op){

case 1:{

n1 = PedirDato();

suma (n1);

i++;

break;

}

case 2:{

n1 = PedirDato();

resta (n1);

i++;

break;

}

case 3:{

n1 = PedirDato();

multiplicacion (n1);

i++;

break;

}

case 4:{

n1 = PedirDato();

division (n1);

i++;

break;

}

case 5:{

printf ("Salir");

break;

}

default: {

printf ("Error");

break;

}

}

}

printf ("Mostrar total:%d", i );

return 0;

}

#include <stdio.h>

int PedirDato(){

    int n;

    printf ("\nEscribe un numero: ");

    scanf ("%i", &n);

    return (n);

}

int suma( int n1, int r ){

    int a;

    a = r + n1;

    printf( "\n%d + %d = %d", r, n1, a );

    return a;

}

int resta (int n1, int r ){

    int a;

    a = r - n1;

    printf( "\n%d - %d = %d", r, n1, a );

    return a;

}

int multiplicacion( int n1, int r ){

    int a;

    a = r * n1;

    printf( "\n%d * %d = %d", r, n1, a );

    return a;

}

int division( int n1, int r ){

    int a;

    a = r / n1;

    printf( " %d / %d = %d", r, n1, a );

    return a;

}

int main(){

    int n1, Op, i;

    int r;

    printf( "\nValor inicial de 'r':" );

    r = PedirDato();

    while( Op!=5 ){

        printf(" \n\n 1:suma, \n 2:resta, \n 3:multiplicacion, \n 4:division, \n 5:salir");

        scanf( "%i", &Op );

        switch( Op ){

            case 1:

                n1 = PedirDato();

                r = suma( n1, r );

                i++;

                break;

            case 2:

                n1 = PedirDato();

                r = resta( n1, r );

                i++;

                break;

            case 3:

                n1 = PedirDato();

                r = multiplicacion( n1, r );

                i++;

                break;

            case 4:

                n1 = PedirDato();

                r = division( n1, r );

                i++;

                break;

            case 5:

                printf ("\n Salir");

                break;

            default:

                printf ("\n Error");

                break;

        }

    }

    printf ("\n\nTotal operaciones realizadas: %d", i );

    printf( "\nValor final de r: %d\n", r );

    return 0;

}