Before writing the C program to check whether a triangle is valid or not if angles are given, we should know the properties of triangles. The angle property of the triangle says that the sum of all three angles should be equal to 180.

#include <stdio.h>

int main()
{
    //variable to store angles
    int angle1, angle2, angle3, sum;

    // Get three angles of triangle from the user
    printf("\n Enter 1 angles of triangle: = ");
    scanf("%d", &angle1);

    printf("\n Enter 2 angles of triangle: = ");
    scanf("%d", &angle2);

    printf("\n Enter 3 angles of triangle: = ");
    scanf("%d", &angle3);

    //Calculate sum of angles
    sum = angle1 + angle2 + angle3;

    //check sum of three angles
    if(sum == 180 && angle1 != 0 && angle2 != 0 && angle3 != 0)
    {
        printf("\n Valid Triangle.\n\n");
    }
    else
    {
        printf("\n Not valid Triangle.\n\n");
    }

    return 0;
}

Output: