Language: C

#include<stdio.h>

int main(void)
{
scanf("%d",&a);
  if(a=a){printf("b");}
  if(a=b){printf("c");}
  if(a=c){printf("d");}
  if(a=d){printf("e");}
  if(a=e){printf("f");}
  if(a=f){printf("g");}
  if(a=g){printf("h");}
  if(a=h){printf("i");}
  if(a=i){printf("j");}
  if(a=j){printf("k");}
  if(a=k){printf("l");}
  if(a=l){printf("m");}
  if(a=m){printf("n");}
  if(a=n){printf("o");}
  if(a=o){printf("p");}
  if(a=p){printf("q");}
  if(a=q){printf("r");}
  if(a=r){printf("s");}
  if(a=s){printf("t");}
  if(a=t){printf("u");}
  if(a=u){printf("v");}
  if(a=v){printf("w");}
  if(a=w){printf("x");}
  if(a=x){printf("y");}
  if(a=y){printf("z");}
  
  return 0;
  
}

Compiler output:
main.c: In function 'main':
main.c:5:13: error: 'a' undeclared (first use in this function)
    5 | scanf("%d",&a);
      |             ^
main.c:5:13: note: each undeclared identifier is reported only once for each function it appears in
main.c:7:8: error: 'b' undeclared (first use in this function)
    7 |   if(a=b){printf("c");}
      |        ^
main.c:8:8: error: 'c' undeclared (first use in this function)
    8 |   if(a=c){printf("d");}
      |        ^
main.c:9:8: error: 'd' undeclared (first use in this function)
    9 |   if(a=d){printf("e");}
      |        ^
main.c:10:8: error: 'e' undeclared (first use in this function)
   10 |   if(a=e){printf("f");}
      |        ^
main.c:11:8: error: 'f' undeclared (first use in this function)
   11 |   if(a=f){printf("g");}
      |        ^
main.c:12:8: error: 'g' undeclared (first use in this function)
   12 |   if(a=g){printf("h");}
      |        ^
main.c:13:8: error: 'h' undeclared (first use in this function)
   13 |   if(a=h){printf("i");}
      |        ^
main.c:14:8: error: 'i' undeclared (first use in this function)
   14 |   if(a=i){printf("j");}
      |        ^
main.c:15:8: error: 'j' undeclared (first use in this function)
   15 |   if(a=j){printf("k");}
      |        ^
main.c:16:8: error: 'k' undeclared (first use in this function)
   16 |   if(a=k){printf("l");}
      |        ^
main.c:17:8: error: 'l' undeclared (first use in this function)
   17 |   if(a=l){printf("m");}
      |        ^
main.c:18:8: error: 'm' undeclared (first use in this function)
   18 |   if(a=m){printf("n");}
      |        ^
main.c:19:8: error: 'n' undeclared (first use in this function)
   19 |   if(a=n){printf("o");}
      |        ^
main.c:20:8: error: 'o' undeclared (first use in this function)
   20 |   if(a=o){printf("p");}
      |        ^
main.c:21:8: error: 'p' undeclared (first use in this function)
   21 |   if(a=p){printf("q");}
      |        ^
main.c:22:8: error: 'q' undeclared (first use in this function)
   22 |   if(a=q){printf("r");}
      |        ^
main.c:23:8: error: 'r' undeclared (first use in this function)
   23 |   if(a=r){printf("s");}
      |        ^
main.c:24:8: error: 's' undeclared (first use in this function)
   24 |   if(a=s){printf("t");}
      |        ^
main.c:25:8: error: 't' undeclared (first use in this function)
   25 |   if(a=t){printf("u");}
      |        ^
main.c:26:8: error: 'u' undeclared (first use in this function)
   26 |   if(a=u){printf("v");}
      |        ^
main.c:27:8: error: 'v' undeclared (first use in this function)
   27 |   if(a=v){printf("w");}
      |        ^
main.c:28:8: error: 'w' undeclared (first use in this function)
   28 |   if(a=w){printf("x");}
      |        ^
main.c:29:8: error: 'x' undeclared (first use in this function)
   29 |   if(a=x){printf("y");}
      |        ^
main.c:30:8: error: 'y' undeclared (first use in this function)
   30 |   if(a=y){printf("z");}
      |        ^