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//bai 1
#include <stdio.h>
int main(){
    int n;
    int a = 0; 
    printf("Nhap so n: ");
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) {
        a += i; 
    }
    printf("Tong cua day tu 1 toi %d la = %d\n", n, a);
    return 0;
}
 
//bai2
#include <stdio.h>
int main(){
    int n;
    int a = 0;
    printf("Nhap so n: ");
    scanf("%d", &n);
    int b = n;
    while (b > 0){
        a++;           
        b = b / 10;  
    }
    printf("So %d co %d chu so.\n", n, a);
    return 0;
}
 
//bai 3
#include <stdio.h>
int main(){
    float diem;
    do{
        printf("Nhap diem kiem tra :");
        scanf("%f", &diem);
    } 
    while (diem < 0 || diem > 10);
    printf("Ban da nhap diem sau: %.1f\n", diem);
    return 0;
}
 
//bai 5
#include <stdio.h>
int main(){
    int n;
    printf("Nhap so nguyen n: ");
    scanf("%d", &n);
    if (n >= 2){
        printf("Cac so nguyen to tu 2 den %d la: ", n);
        for (int i = 2; i <= n; i++){
            int dem = 0;
            for (int j = 1; j <= i; j++) {
                if (i % j == 0) {
                    dem++;
                }
            }
            if (dem == 2) {
                printf("%d ", i);
            }
        }
        printf("\n");
    }
    return 0;
}
 
 
//bai 6
#include <stdio.h>
int main(){
    int n;
    printf("Nhap so hang n: ");
    scanf("%d", &n);
    if (n > 0) {
        for (int i = n; i >= 1; i--) {
            for (int j = 1; j <= i; j++) {
                printf("* ");
            }
            printf("\n");
        }
    } else {
        printf("Vui long nhap lai\n");
    }
    return 0;
}

prog.c:17:5: error: redefinition of ‘main’
 int main(){
     ^~~~
prog.c:3:5: note: previous definition of ‘main’ was here
 int main(){
     ^~~~
prog.c:33:5: error: redefinition of ‘main’
 int main(){
     ^~~~
prog.c:3:5: note: previous definition of ‘main’ was here
 int main(){
     ^~~~
prog.c:46:5: error: redefinition of ‘main’
 int main(){
     ^~~~
prog.c:3:5: note: previous definition of ‘main’ was here
 int main(){
     ^~~~
prog.c:71:5: error: redefinition of ‘main’
 int main(){
     ^~~~
prog.c:3:5: note: previous definition of ‘main’ was here
 int main(){
     ^~~~
prog.c: In function ‘main’:
prog.c:7:5: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ^~~~~~~~~~~~~~~
prog.c: In function ‘main’:
prog.c:21:5: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ^~~~~~~~~~~~~~~
prog.c: In function ‘main’:
prog.c:37:9: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result]
         scanf("%f", &diem);
         ^~~~~~~~~~~~~~~~~~
prog.c: In function ‘main’:
prog.c:49:5: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ^~~~~~~~~~~~~~~
prog.c: In function ‘main’:
prog.c:74:5: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ^~~~~~~~~~~~~~~

Standard output is empty