c programs vishal

programs.c

//Program 1, to reverse strings.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char *argv[])                            //used to accept command line args
{
    if(argc < 2 ){                                          //check if there are any inputs in command line
        printf("please provide inputs");                    //if no, exit
        exit(1);
    }
    char *str = argv[1],temp;                               //get input from command line
    int len = strlen(str),i;
    for(i = 0; i<len/2 ; i++){                              //reverse string, swap first and last values,
       temp = str[i];                                       //then swap second and second last, and so on
       str[i] = str [len-i-1];
       str[len-i-1] = temp;
    } 
    puts(str);                                              //print final output
    return 0;
}


// program to find factorial
#include <stdio.h>
#include <stdlib.h>

long long int fact(long long int n){                        // we use long long int to calculate values for bigger numbers
    return n >= 1 ? n*fact(n-1) : 1;                        // just int can also be used instead of long long int
}                                                           //this function calculates factorial using 
                                                            //recursion and returns the value


int main(int argc, char *argv[])                            //used to accept command line args
{
    if(argc < 2 ){                                          //check if there are any inputs in command line
        printf("please provide inputs");                    //if no, exit
        exit(1);
    }
    if(argv[1]>0){                                          //check if the input is greater than 0 if yes print factorial.
        printf("%lld", fact(atoi(argv[1])));                //atoi(...) is used to convert ascii input to integer.
    } else {
        printf("Enter a number greater than 0");            //if input less than 0, exit
        exit(1);
    }
    return 0;
}



//program to check prime
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main(int argc, char *argv[])                            //used to accept command line args
{
    if(argc < 2 ){                                          //check if there are any inputs in command line
        printf("please provide inputs");                    //if no, exit
        exit(1);
    }
    int num = atoi(argv[1]);                                //atoi(...) is used to convert ascii input to integer.
    int lim = ceil(sqrt(num)), flag = 0, i;                 //find square root
                                                            
    for(i = 2; i < lim; i++){                               //check if prime
        if(flag) break;
        if (num%i == 0) flag = 1;
    }
    printf("%s", flag == 0 ? "prime" : "composite");      //print result
    return 0;
}

//program to find area of circle with given radius
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])                            //used to accept command line args
{
    if(argc < 2 ){                                          //check if there are any inputs in command line
        printf("please provide inputs");                    //if no, exit
        exit(1);
    }
    int radius = atoi(argv[1]);                             //atoi(...) is used to convert ascii input to integer.
    printf("%f", 3.14*radius*radius);                       //print 3.14 * radius^2
    return 0;
}