Factorial program in c

Question

Trying to make a code that gets the factorial of the inputted number.

int factorial(int number, int i)
{
    int endval;
    for(i = number - 1; i>0; i--){
        endval = number * i;
    }
    if (endval == 0){
        printf("1");
    }
    return endval;
}

int main()
{
    int endvalue, numA, numB;
    char userchoice[1];
    printf("Enter a choice to make (f for factorial): \n");
    scanf("%s", userchoice);
    if(strcmp(userchoice, "f")== 0){
        printf("Enter a value to get it's factorial: ");
        scanf("%d", &numA);
        endvalue = factorial(numA, numB);
        printf("%d", endvalue);
        return 0;}


    getch();
    return 0;
}

For some reason the whole for loop doesn't do anything in the function when I set the answer (number*i)= endval. It just prints out the same number I inputted and gives me an absurd answer for 0!.

int factorial(int number, int i)
{
    int endval;
    for(i = number - 1; i>0; i--){
            endval = number * i;
    }
    if (endval == 0){
        printf("1");
    }
    return endval;
}

However the code works perfectly fine when I remove endval variable entirely (with the exception that it gets 0! = 10)

int factorial(int number, int i)
{
    for(i = number - 1; i>0; i--){
        number = number * i;
    }
    if (number == 0) {printf("1");}
    return number;
}

Is there anything I missed in the code that's causing these errors?

Answer 1

#include <stdio.h>
#include <string.h>

int factorial(int number)
{
    int endval=1;
    for(int i = number ; i>0; i--){
        endval *= i;
    }
    return endval;
}

int main()
{

    int endvalue=0;
    int numA=0;

    char userchoice[1];
    printf("Enter a choice to make (f for factorial): ");
    int ret=scanf("%s", userchoice);
    if (!ret){
        printf("Error in scanf: %d", ret);
    }
    if(strcmp(userchoice, "f")== 0){
        printf("Enter a value to get it's factorial: ");
        scanf("%d", &numA);
        endvalue = factorial(numA);
        printf("%d", endvalue);
        return 0;
    }

    getchar();
    return 0;
}

Code with some changes will work

• factorial() function can get only one argument.
• As a good habit all variables must be initialized.
• Add include statement to source and be explicit not rely on compiler. As we use strcmp() we must include string.h
• use standard getchar() instead of getch()
• Also can check return value of library function scanf() to ensure reading is correct or not.
• You can use warnings from compiler to get most of above notes. In gcc: gcc -Wall code.c
• Use a debugger to run program line by line and monitor variables value in each steps or use as many printf() to see what happens in function call.