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#include <stdio.h>
 
int n, r;
 
int factorial (int n)
{
    if (n==0)
        return 1;
    else if (n>0)
        return n*factorial(n-1);
        return 0;
    else
        printf("음수는 계산할 수 없습니다\n");
}
 
int nPr (int n, int r)
{
    if (n<0 or r<0)
        printf("음수는 입력할 수 없습니다\n");
        return 0;
    else if (r>n)
        printf("r은 n보다 클 수 없습니다\n");
        return 0;
    else if (r==0)
        return 1;
    else
        return (n*factorial(n-1))/((n-r)*factorial(n-r-1));
}
 
int nCr (int n, int r)
{
    if (n<0 or r<0)
        printf("음수는 입력할 수 없습니다\n");
        return 0;
    else if (r>n)
        printf("r은 n보다 클 수 없습니다\n");
        return 0;
    else if (r==0)
        return 1;
    else
        return (n*factorial(n-1))/((r&factorial(r))*((n-r)*factorial(n-r-1)));
}
 
int main (void)
{
    int select;
    printf("계산할 방식을 선택하세요\n");
    printf("----------\n");
    printf("1.팩토리얼\n2.nPr\n3.nCr\n");
    printf("----------\n");
    scanf("숫자 입력: %d\n", &select);
 
    switch(select)
    {
    case 1 :
        int n;
        printf("팩토리얼 계산기\n");
        scanf("n값을 입력하세요: %d", &n);
        printf ("%d!=%d", n, factorial(n));
        break;
    case 2 :
        int n,r;
        printf("nPr 계산기\n");
        scanf("n값을 입력하세요: %d", &n);
        scanf("r값을 입력하세요: %d", &r);
        printf("%dP%d=%d", n, r,nPr(n, r));
        break;
    case 3 :
        int n,r;
        printf("nCr 계산기\n");
        scanf("n값을 입력하세요: %d", &n);
        scanf("r값을 입력하세요: %d", &r);
        printf("%dC%d=%d", n, r,nCr(n, r));
        break;
    default:
        printf("다시 입력하세요\n");
    }
    return 0;
}

prog.cpp: In function ‘int factorial(int)’:
prog.cpp:12:5: error: ‘else’ without a previous ‘if’
     else
     ^~~~
prog.cpp: In function ‘int nPr(int, int)’:
prog.cpp:21:5: error: ‘else’ without a previous ‘if’
     else if (r>n)
     ^~~~
prog.cpp:24:5: error: ‘else’ without a previous ‘if’
     else if (r==0)
     ^~~~
prog.cpp: In function ‘int nCr(int, int)’:
prog.cpp:35:5: error: ‘else’ without a previous ‘if’
     else if (r>n)
     ^~~~
prog.cpp:38:5: error: ‘else’ without a previous ‘if’
     else if (r==0)
     ^~~~
prog.cpp: In function ‘int main()’:
prog.cpp:62:13: error: redeclaration of ‘int n’
         int n,r;
             ^
prog.cpp:56:13: note: ‘int n’ previously declared here
         int n;
             ^
prog.cpp:69:13: error: redeclaration of ‘int n’
         int n,r;
             ^
prog.cpp:56:13: note: ‘int n’ previously declared here
         int n;
             ^
prog.cpp:69:15: error: redeclaration of ‘int r’
         int n,r;
               ^
prog.cpp:62:15: note: ‘int r’ previously declared here
         int n,r;
               ^

Standard output is empty