#include <stdio.h>

#define STRLEN  20

int main(void) {
    char conv[25]={
        '2','2','2',
        '3','3','3',
        '4','4','4',
        '5','5','5',
        '6','6','6',
        '7','7','7','7',
        '8','8','8',
        '9','9','9'
    };
    char str[STRLEN];

    fgets(str, sizeof(str), stdin);

    int i=0;
    while ((i<STRLEN)&&(str[i] != '\n')) {
        if ((str[i] >= 'A')&&(str[i] <= 'Y')&&(str[i] != 'Q')) {
            printf("%c", conv[str[i]-'A']);
        } else {
            printf("%c", str[i]);
        }
        i++;
    }

    return 0;
}

不做防呆,簡單用Python

 #!/usr/bin/env python3

alphanum = {'A': '2', 'B': '2', 'C': '2',
            'D': '3', 'E': '3', 'F': '3',
            'G': '4', 'H': '4', 'I': '4',
            'J': '5', 'K': '5', 'L': '5',
            'M': '6', 'N': '6', 'O': '6',
            'P': '7', 'R': '7', 'S': '7',
            'T': '8', 'U': '8', 'V': '8',
            'W': '9', 'X': '9', 'Y': '9'
           }

def tran(x):
  if x == '-':
    return x
  else:
    return alphanum[x]

lst = 'A-BDG-WWX'
print(lst)
print( ''.join(list(map(tran, lst))))

result:

|=> ./dictmap1.py 
A-BDG-WWX
2-234-999

單純考慮資料擴充的方便性，用 map + array的寫法 (Javascript)
演算法可以再優化

let digitalCharMap = {
    '-': ['-'],
    '2': ['A', 'B', 'C'],
    '3': ['D', 'E', 'F'],
    '4': ['G', 'H', 'I'],
    '5': ['J', 'K', 'L'],
    '6': ['M', 'N', 'O'],
    '7': ['P', 'R', 'S'],
    '8': ['T', 'U', 'V'],
    '9': ['W', 'X', 'Y']
}

function getIntOfString (inputString) {
    let result = ''

    for (let singleChar of inputString ) {
      let isExists = false

      for (let numKey in digitalCharMap) {
        if (digitalCharMap[numKey].indexOf(singleChar) >= 0) {
          result += numKey
          isExists = true
        }
      }

      if (isExists !== true) {
          return `${singleChar} is not exists`
      }
    }
    return result
}


console.log(getIntOfString('ADA-B'))
//output: "232-2"

console.log(getIntOfString('ADZ-B'))
//output: "Z is not exists"

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