Question

Please help me to write a program to check telephone number validity . （just check all characters are "0"~"9"）
1.C language
2.Please use "printf"（no scanf、gets....）
3.only argv ,argc accepted
4.Please explain the steps （cause I'm a beginner hhhhh）
Thank you soooooo much!!!!!

Answer 1

/*

To check a valid phone number we need to check digits, length, country code and starting digit of phone number.

But in your case you need to check only whether It contains all digits or not.

So to check this you can follow below simple simple steps
1. Declare a boolean variable and assigne true value to it.
2. Iterate over each character of the input
3. Check if current character in 0 to 9 character range
4. If all are digits then correct otherwise incorrect.

As your question instructed that we can not use any function other than printf so we need to use command line arguments.

argc: refers to the number of arguments passed by the user including the name of the program.
argv[]: is a pointer array which points to each argument passed to the program

argv[0]: name of the program
argv[1]: First argument to the program

Sample Input:
9090909

Sample Output:
The argument supplied is 9090909
Valid phone nnumber

*/

/**************************Execution Steps**********************************************
1. Copy the code from below #include<sdtio.h> till last to the you ide/editor
2. Save the code as Telecomvalidation.c
3. Compile the code using command gcc Telecomvalidation.c
4. Run the program using command ./Telecomvalidation 909840945
  
If still not clear, Please ask you friend or search on google "How to execute c program in linux"
  
*/

/***************Your program start from below line******************************/

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

int main( int argc, char *argv[] ) {

int i,len,flag=0;
//you can change the size of array based on length of telephone no
char telphno[10];
printf("Program name : %s\n", argv[0]);

if( argc == 2 ) {
printf("The argument supplied is %s\n", argv[1]);
//Getting the length of the phone number
len=strlen(argv[1]);
  
//copying first argument to the new variable telphno
strcpy(telphno,argv[1]);
  
//Iterating over each character and checking whther a character is in the range of character 0 to 9
//If in range then continue else updating flag value and breaking the loop
for(i=0;i<len;i++)
{
if(telphno[i]<'0' || telphno[i]>'9')
{
flag=1;
break;
}
}
//Printing the output.
if(flag==1)
printf("Invalid phone nnumber\n");
else
printf("Valid phone nnumber\n");
}
else if( argc > 2 ) {
printf("Too many arguments supplied.\n");
}
else {
printf("One argument expected.\n");
}
}