C++ program to convert string to numeric digits - c++

Question

I'm trying to create a function that converts input words to numeric digits like a mobile numpad. It is for an assignment. I cannot use cstring or character arrays.
Can someone please identify and correct the error in my code? It currently gives the error: ISO C++ forbids comparison between pointer and integer [-fpermissive].
I am not using any pointer variables. I do have used the strlen() function to determine the exact place of a character in a string. Any help is greatly appreciated.
#include<iostream>
#include<conio.h>
#include<string.h>
#include<stdio.h>
using namespace std;
void Letter_correspondence();
int main()
{
Letter_correspondence();
return 0;
}
void Letter_correspondence()
{
cout<<"Enter the letters of the word you want to convert to numbers: ";
char a[]="Hello";
char b[]="world";
int len=strlen(a);
int lenb=strlen(b);
int n;
int l=a[n];
for (n=0;n<=7;n++)
{
while (n<=len)
{
if (l=="a"||l=="b"||l=="c")
{
if (n==2)
{
cout<<"-";
}
cout<<"2";
}
else if (l=="d"||l=="e"||l=="f")
{
if (n==2)
{
cout<<"-";
}
cout<<"3";
}
else if (l=="g"||l=="h"||l=="i")
{
if (n==2)
{
cout<<"-";
}
cout<<"4";
}
else if (l=="j"||l=="k"||l=="l")
{
if (n==2)
{
cout<<"-";
}
cout<<"5";
}
else if (l=="m"||l=="n"||l=="o")
{
if (n==2)
{
cout<<"-";
}
cout<<"6";
}
else if (l=="p"||l=="q"||l=="r"||l=="s")
{
if (n==2)
{
cout<<"-";
}
cout<<"7";
}
else if (l=="t"||l=="u"||l=="v")
{
if (n==2)
{
cout<<"-";
}
cout<<"8";
}
else if (l=="w"||l=="x"||l=="y"||l=="z")
{
if (n==2)
{
cout<<"-";
}
cout<<"9";
}
}
}
}

Answer 1

If I understood this right, you're trying to map characters to different ones and print them. You said you cannot use cstring or character arrays, but you do that here:
char a[]="Hello";
char b[]="world";
Instead, I would just use std::string:
std::string a = "Hello";
You can then iterate through it using a range-based for loop. The best way to print your string would probably be using a switchstatement:
for (char &c : a)
{
switch (tolower(c)) {
case 'a':
case 'b':
case 'c':
std::cout << 2;
break;
case 'd':
case 'e':
case 'f':
std::cout << 3;
break;
case 'g':
case 'h':
case 'i':
std::cout << 4;
break;
case 'j':
case 'k':
case 'l':
std::cout << 5;
break;
case 'm':
case 'n':
case 'o':
std::cout << 6;
break;
case 'p':
case 'q':
case 'r':
case 's':
std::cout << 7;
break;
case 't':
case 'u':
case 'v':
std::cout << 8;
break;
case 'w':
case 'x':
case 'y':
case 'z':
std::cout << 9;
break;
default:
std::cout << c;
}
}
If you're using an old version of C++ that doesn't support range based for loops, change this
for (char &c : a)
{
switch (tolower(c)) {
To this
for (size_t i = 0; i < a.size(); i++)
{
switch (tolower(a[i])) {
And std::cout << c; to std::cout << a[i];.