CMD line calculation PGM

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

int valid(char s[]){
        int valid = 0;
        int cnt = 0;
        int i;
        for(i = 0;i < strlen(s);i++){
                if(s[i] >= '0' && s[i] <= '9'){
                        valid = 1;
                }
                else if(s[i] == '.')
                        cnt++;
                else{
                        valid = 0;
                        break;
                }
        }
        if(cnt > 1)
                valid = 0;
        if(valid == 0){
                printf("Plz enter valid numbers!\n");
                exit(1);
        }
        return valid;
}

int main(int argc,char * argv[]){
        double num1;
        double num2;
        if(argc!=3){
                printf("Plz enter two numbers!!\n");
        exit(0);
        }

        if((valid(argv[1])) && (valid(argv[2]))){
                sscanf(argv[1],"%lf",&num1);
                sscanf(argv[2],"%lf",&num2);
        }

        printf("answer: %lf \n",num1+num2);
/*                                      num1-num2
                                        num1*num2

        To get num1/num2 need to validate that the num2 cant not be zero.
*/
        return 2;
}