C Program to check whether a string is Pangram

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

int main(){
int flag,i,n;
flag=0;i=0;
char str[100],modstr[100];
int ar[256]={0};
printf("Enter the string:\n");
fgets(str,100,stdin);


while(str[i]){
modstr[i]=toupper(str[i]);
i++;
}
i=0;
while(modstr[i]){
ar[modstr[i]]=1;
i++;
}

for(i='A';i<='Z';i++){
if(ar[i]==0){
flag=1;
break;
}
}


if(flag==1){
printf("\nNot a Panagram");
}
else
printf("\nString is a Panagram");
return 0;
}