Probleme Lab 2

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

int char_occurence(char s[], char c) {
    int ct=0;
    for(int i=0;i<strlen(s);i++)
    if (s[i]==c)
        ct++;
    return ct;
}

int valid_triangle(float a, float b, float c) {
    if (a<0&&b<0&&c<0)
        return 0;
    if (a+b<c)
        return 0;
    if (b+c<a)
        return 0;
    if (a+c<b)
        return 0;
}

double function_value(double f[], double x, int n) {
    double sum=0;
    for (int i=0;i<n;i++) {
        sum+=f[i]*pow(x,i);
        printf("%f\n", sum);
    }
    return sum;
}

void function_derivative(double f_init[], double f_final[], int n) {
    for(int i=0;i<n;i++) {
        f_final[i]=i*f_init[i];
    }
    return;
}

int main()
{
    char s[50],c;
    double f[3]={2,4,6},x=3,n=5;
    double f_init[5]={3,7,2,6,8},f_final[5];
    function_derivative(f_init,f_final,n);
    printf("Function's derivative coeffs are:");
    for (int i=0;i<n;i++)
        printf("%f ", f_final[i]);
    printf("The final sum is %f", function_value(f,x,n));
    gets(s);
    scanf("%c", &c);
    printf("Function found character \"%c\" %d times in the string", c, char_occurence(s,c));
    return 0;
}