Question

I have a triangle program in c

#include <stdio.h>

// A function which decides the type of the triangle and prints it
void checkTriangle(int s1, int s2,int s3)
{
    // Check the values whether it is triangle or not.
    if ((s1 + s2 > s3 && s1 +  s3 > s2 && s2 + s3 > s1) && (s1 > 0 && s2 > 0 && s3 > 0))
    {
        // Deciding type of triangle according to given input.
        if (s1 == s2 && s2 == s3)
            printf("EQUILATERAL TRIANGLE");
        else if (s1 == s2 || s2 == s3 || s1 == s3)
            printf("ISOSCELES TRIANGLE\n");
        else
            printf("SCALENE TRIANGLE \n");
    }
    else
        printf("\nTriangle could not be formed.");
}

int main(void)
{
    // Initializing variables
    int a,b,c;

    // Getting input from user
    printf("Please enter the sides of triangle");

    printf("\nPlease enter side 1:");
    scanf("%d",&a);

    printf("Please enter side 2:");
    scanf("%d",&b);

    printf("Please enter side 3:");
    scanf("%d",&c);

    // Calling function in order to print type of the triangle.
    checkTriangle(a,b,c);
}

When the input is:

7b

it gives an error, which is what I want, but when I entered the data like this:

7
7
7b 

it ignores ‘b’ and take 7 as an integer — but why? How can I prevent this?

What I want to do is give an error also for

7
7
7b

Answer 1

If you want to be able to detect an error with the user’s input, such as a line not being a valid decimal integer, then you could do the following:

• Read the input into a buffer using fgets(buffer, size, stdin)
• Use strtoul(buffer, &endptr, 10) to parse the buffer as a decimal integer (base 10), where endptr is a char*
• endptr will point to the first invalid character in buffer, ie. the character after the last one which was successfully parsed
• Now if *endptr == '\0', ie. endptr points to the end of buffer, the whole string was parsed as a valid decimal integer